research on blood types

The Mystery of Human Blood Types

The ABO blood group evolved at least 20 million years ago, but scientists still don’t understand the purpose of blood types

Erin Wayman

Blood banks run blood type tests before blood is sent to hospitals for transfusions. Image: U.S. Navy photo by Mass Communication Specialist 3rd Class Jake Berenguer/Wikicommons

Everyone’s heard of the A, B, AB and O blood types. When you get a blood transfusion, doctors have to make sure a donor’s blood type is compatible with the recipient’s blood, otherwise the recipient can die. The ABO blood group, as the blood types are collectively known, are ancient. Humans and all other apes share this trait, inheriting these blood types from a common ancestor at least 20 million years ago and maybe even earlier, claims a new study published online today in Proceedings of the National Academy of Sciences . But why humans and apes have these blood types is still a scientific mystery.

The ABO blood group was discovered in the first decade of the 1900s by Austrian physician Karl Landsteiner . Through a series of experiments, Landsteiner classified blood into the four well-known types. The “type” actually refers to the presence of a particular type of antigen sticking up from the surface of a red blood cell. An antigen is anything that elicits a response from an immune cell called an antibody. Antibodies latch onto foreign substances that enter the body, such as bacteria and viruses, and clump them together for removal by other parts of the immune system. The human body naturally makes antibodies that will attack certain types of red-blood-cell antigens. For example, people with type A blood have A antigens on their red blood cells and make antibodies that attack B antigens; people with type B blood have B antigens on their red blood cells and make antibodies that attack A antigens. So, type A people can’t donate their blood to type B people and vice versa. People who are type AB have both A and B antigens on their red blood cells and therefore don’t make any A or B antibodies while people who are type O have no A or B antigens and make both A and B antibodies. (This is hard to keep track of, so I hope the chart below helps!)

After Landsteiner determined the pattern of the ABO blood group, he realized blood types are inherited, and blood typing became one of the first ways to test paternity. Later, researchers learned ABO blood types are governed by a single gene that comes in three varieties: A, B and O. (People who are type AB inherit an A gene from one parent and a B gene from the other.)

This chart lists the antigens and antibodies made by the different ABO blood types. Image: InvictaHOG/Wikicommons

More than a hundred years after Landsteiner’s Nobel Prize-winning work, scientists still have no idea what function these blood antigens serve. Clearly, people who are type O— the most common blood type —do just fine without them. What scientists have found in the last century, however, are some interesting associations between blood types and disease. In some infectious diseases, bacteria may closely resemble certain blood antigens, making it difficult for antibodies to detect the difference between foreign invaders and the body’s own blood. People who are type A, for instance, seem more susceptible to smallpox, while people who are type B appear more affected by some E. coli infections.

Over the last hundred years, scientists have also discovered that the ABO blood group is just one of more than 20 human blood groups . The Rh factor is another well known blood group, referring to the “positive” or “negative” in blood types, such as A-positive or B-negative. (The Rh refers to Rhesus macaques , which were used in early studies of the blood group.) People who are Rh-positive have Rh antigens on their red blood cells; people who are Rh-negative don’t and produce antibodies that will attack Rh antigens. The Rh blood group plays a role in the sometimes fatal blood disease erythroblastosis fetalis that can develop in newborns if an Rh-negative women gives birth to an Rh-positive baby and her antibodies attack her child.

Most people have never heard of the numerous other blood groups—such as the MN , Diego , Kidd and Kell —probably because they trigger smaller or less frequent immune reactions. And in some cases, like the MN blood group, humans don’t produce antibodies against the antigens. One “minor” blood type that does have medical significance is the Duffy blood group . Plasmodium vivax , one of the parasites that causes malaria, latches onto the Duffy antigen when it invades the body’s red blood cells. People who lack the Duffy antigens, therefore, tend to be immune to this form of malaria.

Although researchers have found these interesting associations between blood groups and disease, they still really don’t understand how and why such blood antigens evolved in the first place. These blood molecules stand as a reminder that we still have a lot to learn about human biology.

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Erin Wayman | | READ MORE

Erin Wayman is a science and human evolution blogger for Hominid Hunting. She has M.As in biological anthropology and science writing.

A new understanding of how your blood type influences your health

We now know that there are at least 45 different blood types and that yours may influence your risk of disease, from malaria to cancer

By David Cox

23 January 2024

Researchers have recently discovered our 45th blood type

PhotoAlto/Alamy

IN 2023, a paper was published in the journal Blood that ended a mystery stretching back four decades. It detailed the existence of a new blood type , first proposed in the 1980s – and of which there are now 45 to date.

This particular discovery was born from tragedy. A baby died suddenly shortly after birth. Its mother was subsequently discovered to have a blood type (or group) that had never been identified before, whereas the baby had inherited its father’s. The two blood groups interacted in a rare way that led to a fatal inflammatory response.

Are you truly healthy? These new tests provide the ultimate check-up

It reflects a long-standing mystery of the human body – just how many blood types there really are, and how this part of our physiology will evolve in the future. We are making headway: our recently improved understanding of the differences in our blood is helping to make transfusions safer and even starting to reveal how your blood group influences your health.

How many blood types are there?

Blood types are distinguished by what kind of antigens are attached to red blood cells and what kind of antibodies are in the surrounding plasma. The four most common blood groups are A, B, O and AB, which relate to combinations of antigens and antibodies, but delve a little deeper and there is astonishing complexity. Currently, the 45 blood types represent more than 390 different antigens and antibodies, with new discoveries being made all the time.

This…

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Blood Types: What Letters, Positive, and Negative Signs Mean

What to Know About Your Blood Type

Blood Types
Why to Know Your Type
Compatibility
Significance in Pregnancy
Finding Your Blood Type

Your blood type is a combination of letters and signs identifying antigens present or absent on the surface of your red blood cells. Antigens are substances that can trigger the immune system to produce antibodies. Antibodies are proteins that lead an attack on substances perceived as foreign "invaders."

Blood typing is essential if you need to receive a blood transfusion . Your antibodies can attack transfused red blood cells of incompatible types. Mixing certain blood types can have dangerous health consequences. Some types of blood are more common than others, and they vary in compatibility.

This article will discuss how blood types are identified, how rare or common they are, and what that means for you.

Illustration by Lara Antal for Verywell Health

How Many Blood Types Are There?

The ABO system has four major blood types: A, B, AB, and O. Blood types are further categorized by the presence (positive or +) or absence (negative or -) of the Rh(D) antigen on the surface of their red blood cells, also known as the Rh factor . This produces the eight major blood types.

A and B antigens are sugars. The type of sugar antigens a person has determines whether they have A, B, or a mix of A and B (AB). If they lack both A and B, they are type O.

Protein antigens identify if you have a negative or positive Rh factor. A plus (+) or minus (-) sign indicates the presence or absence of the Rh factor. The plus indicates the presence of the antigen, while the minus means it is not widely present. About 85% of the population is Rh positive.

The International Society of Blood Transfusion further divides blood types into blood group systems by other types of antigens that may be present. They have identified 45 different blood group systems with hundreds of different antigens.

Some blood types are found in a limited number of people. In the United States, the blood types each found in less than 5% of the population are:

AB- : 0.6% of the population
B- : 1.5% of the population
AB+ : 3.4% of the population

Most Common

More than 70% of the people in the United States have one of these two common blood types:

O+ : 37.4% of the population
A+ : 35.7% of the population

What Is Golden Blood?

Golden blood is the rarest known type of blood in the world. It has no Rh antigens at all, known as Rh null . It is dubbed "golden blood" because it can be donated to people with almost any Rh blood type, including those with rare types of Rh antigens.

However, if people with golden blood need blood, they can only receive the same type of blood. Experts estimate that only about 50 people are known to have golden blood, which was first detected in Australian aboriginal people.

Reasons to Know Your Blood Type

If you need blood during surgery or due to an injury or illness, it's essential to receive blood of a type that is compatible with your own. The hospital laboratory will type your blood and match it to donor units to ensure you only receive compatible blood.

Otherwise, you may have a hemolytic transfusion reaction when your immune system detects foreign proteins on the cells of an incompatible blood type and attempts to destroy them. Transfusion reactions range from mild to life-threatening. They can appear right after a transfusion or up to weeks later.

You can also help others by knowing your blood type in case you are in a position to donate to another individual in need or because blood bank supplies of your type of blood are low.

Different blood types also appear to make people more or less likely to develop certain conditions, including kidney stones, high blood pressure during pregnancy, and bleeding disorders. One study found people with blood group A have a higher likelihood of infection with COVID-19 than those in blood group O.

Compatibility of Different Blood Types

Compatible blood types are based on whether the recipient has antibodies to the donor blood antigens or may develop them.

Early in life, your immune system forms antibodies against A or B antigens not present on your red blood cells. People with blood type A will have anti-B antibodies, and those with type B blood will have anti-A antibodies. Type O blood has both anti-A and anti-B antibodies. Type AB blood has neither A nor B antibodies.

Antibodies only form against the Rh factor if an Rh negative person is exposed to Rh positive blood due to transfusion or pregnancy. The following chart shows what types of blood are compatible with each other.

Universal Donors and Recipients

Type O negative blood is called a universal donor , meaning that it can be safely given to people with most other blood types and has a low risk of a transfusion reaction. People with type AB positive blood are known as universal recipients, meaning they can be given almost any type of blood safely.

Unless blood is needed immediately to save a person's life, the hospital laboratory will type the person's blood and perform compatibility testing with the donor blood units (crossmatching) to ensure the safety of the transfusion.

Testing Blood Types in Pregnancy

If you are pregnant, it's important to identify your Rh blood type so you and your healthcare providers can prevent the consequences of Rh incompatibility. This affects only pregnant people who are Rh negative.

If the pregnant person is Rh negative and the other parent is Rh positive, the fetus may be Rh positive. This is called Rh incompatibility.

This incompatibility will not affect a child born during a first incompatible pregnancy. During birth, however, the blood of the pregnant person and fetus mixes. The Rh negative pregnant person can develop antibodies to the Rh factor.

Those antibodies could harm subsequent fetuses that are Rh positive. The pregnant person's anti-Rh(D) antibodies will identify fetal Rh proteins as foreign and attack them. Fetal red blood cells can swell and tear in response, known as hemolytic disease of the fetus and newborn .

This can lower the fetus's or newborn's red blood cell count and lead to serious consequences, such as brain damage, pregnancy loss, or death of the newborn.

An Rh negative pregnant person who has not developed anti-Rh(D) antibodies should given RhoGAM, or intravenous WinRho, a Rho(D) immune globulin to prevent the development of the antibodies.

How to Find Out Your Blood Type

A blood test can determine your blood type . If you donate blood or plasma , blood typing will be performed at no charge. You can learn your blood type from the report of the donor service.

Blood typing is not a part of routine blood tests. It's commonly ordered if you are having surgery, need a blood transfusion or organ transplant, or are pregnant.

You could request a blood type test from your healthcare provider, but it may not be covered by health insurance if it isn't medically necessary. At a healthcare facility, a small amount of blood will be drawn and sent to a lab for testing.

Check your medical record to see if a blood type test was done in the past and is reported there. If you are unsure how to access your medical record, ask your healthcare provider.

Home blood type tests are available in most states. They are generally accurate if performed correctly. Saliva tests are another option, but they may be more costly and less accurate.

While your blood type doesn't change, a blood type test will be performed each time you need a transfusion. An incompatible transfusion can be fatal, so extreme care is taken to ensure you receive only compatible units.

Blood typing is reported using the ABO blood system and the presence or absence of the Rh(D) antigen known as the Rh factor, resulting in eight major blood types. Some blood types are much more common than others.

If someone needs a blood transfusion, it is essential to use the same or a compatible type of blood to avoid potentially serious reactions to a transfusion. Pregnant people and their healthcare providers must know their Rh factor status to avoid hemolytic disease of the fetus and newborn.

Professional laboratory blood typing is more reliable than home tests, though home blood type tests are available.

Stanford Blood Center. Blood types.

International Society of Blood Transfusion. Red cell immunogenetics and blood group terminology.

Stanford Blood Center. Blood types .

Australian Academy of Science. Rare blood types .

MedlinePlus. Hemolytic transfusion reaction.

Dahlén T, Clements M, Zhao J, Olsson ML, Edgren G. An agnostic study of associations between ABO and RhD blood group and phenome-wide disease risk . Ginsburg D, Wittkopp PJ, Desch KC, eds. eLife. 2021;10:e65658. doi:10.7554/eLife.65658.

Wu SC, Arthur CM, Jan HM, et al. Blood group A enhances SARS-CoV-2 Infection . Blood . 2023;142(8):742-747. doi:10.1182/blood.2022018903

National Library of Medicine. The ABO blood group.

American College of Obstetricians and Gynecologists. The Rh factor: how it can affect your pregnancy.

Myle AK, Al-Khattabi GH. Hemolytic disease of the newborn: a review of current trends and prospects . Pediatric Health Med Ther. 2021;12:491-498. doi:10.2147/PHMT.S327032

Eldon Biologicals A/S. Eldoncard: home blood type testing kit .

Velani PR, Shah P, Lakade L. Determination of ABO blood groups and Rh typing from dry salivary samples. Int J Clin Pediatr Dent . 2018;11(2):100-104. doi:10.5005/jp-journals-10005-1493

By Nancy LeBrun LeBrun is a Maryland-based freelance writer and award-winning documentary producer with a bachelor's degree in communications.

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Scientists Have Discovered a New Set of Blood Groups

The unborn baby was in trouble. Its mother’s doctors, at a UK hospital, knew there was something wrong with the fetus’s blood, so they decided to perform an emergency C-section many weeks before the baby was due. But despite this, and subsequent blood transfusions, the baby suffered a brain hemorrhage with devastating consequences. It sadly passed away.

It wasn’t clear why the bleeding had happened. But there was a clue in the mother’s blood, where doctors had noticed some strange antibodies. Some time later, as the medics tried to find out more about them, a sample of the mother’s blood arrived at a lab in Bristol run by researchers who study blood groups.

They made a startling discovery: The woman’s blood was of an ultrarare type, which may have made her baby’s blood incompatible with her own. It’s possible that this prompted her immune system to produce antibodies against her baby’s blood—antibodies that then crossed the placenta and harmed her child, ultimately leading to its loss. It may seem implausible that such a thing could happen, but many decades ago, before doctors had a better understanding of blood groups, it was much more common .

Through studying the mother’s blood sample, along with a number of others, scientists were able to unpick exactly what made her blood different, and in the process confirmed a new set of blood grouping—the “Er” system, the 44th to be described.

You’re probably familiar with the four main blood types—A, B, O, and AB. But this isn’t the only blood classification system. There are many ways of grouping red blood cells based on differences in the sugars or proteins that coat their surface, known as antigens. The grouping systems run concurrently, so your blood can be classified in each—it might, for instance, be type O in the ABO system, positive (rather than negative) under the Rhesus system, and so on.

Thanks to differences in antigens, if someone receives incompatible blood from a donor, for example, the recipient’s immune system may detect those antigens as foreign and react against them. This can be highly dangerous, and is why donated blood needs to be a suitable match if someone is having a transfusion.

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On average, one new blood classification system has been described by researchers each year during the past decade. These newer systems tend to involve blood types that are mind-bogglingly rare but, for those touched by them, just knowing that they have such blood could be lifesaving. This is the story of how scientists unraveled the mystery of the latest blood system—and why it matters.

It was back in 1982 that researchers first described an unusual antibody in a blood sample that hinted that this mystery blood type was out there. The scientists couldn’t go much further than that at the time, but they knew that the antibody was a clue pointing toward some unknown molecule or structure that prompted the person’s immune system to generate it.

In the years that followed, more people with these unusual antibodies turned up—but only now and again. Generally, these people surfaced thanks to blood tests containing the mysterious and rare antibodies. Eventually, Nicole Thornton and her colleagues at NHS Blood and Transplant in the United Kingdom decided to look into what might be behind the antibodies. “We work on rare cases,” she says. “It starts off with a patient with a problem that we’re trying to resolve.”

But so rare were the mysterious antibodies in the latest work that when the team started their investigation, they had historical blood samples from just 13 people—gathered over 40 years—to analyze. Other recently established systems have been found thanks to similarly small numbers of people. Back in 2020, Thornton and her colleagues described a new blood group called MAM-negative that at the time was confirmed in just 11 people worldwide. And some of the most recently discovered blood groups have been found in single families, she adds. Both “MAM” and “Er” are obscure references to the names of the patients whose blood samples first sparked the possibility of a new blood group discovery.

It turns out that the new, 44th grouping system, detailed in the journal Blood , is tied to a particular protein found on the surface of red blood cells.

Originally, Thornton had an inkling this protein, called Piezo1, was involved after she compared the genomes of patients in the study. She and colleagues noticed how the gene responsible for this protein varies across people with different Er blood types. Due to those genetic differences, a small number of people have alternative amino acids, or building blocks, in their Piezo1 protein. Blood cells with the more common Piezo1 protein seem foreign to their bodies’ immune systems as a result.

The team then checked to see whether antibodies reacted with lab cultures that either did or did not contain mutant versions of the Piezo1 protein, which they created using gene editing. That allowed them to confirm that variation in Piezo1 really was the driver of blood incompatibility in the people whose samples they were looking at. “It was something you couldn’t have done a few years ago,” says coauthor Ash Toye, professor of cell biology at the University of Bristol.

There are five Er antigens in total—five possible variations of Piezo1 on the surface of red blood cells that can lead to incompatibility. Two of the antigens were newly described by Thornton and her fellow researchers, and one of those was found in blood from the pregnant woman in the UK who lost her baby.

The results of the study will likely be officially ratified as defining a new blood group system later this year, at a meeting of the International Society of Blood Transfusion. The effort required to make the discovery was “massive,” says Neil Avent, honorary professor in the blood diagnostics group at the University of Plymouth, who was not involved in the work. It also revealed complexities about this rare blood—for instance, that there are multiple genetic mutations associated with it.

Across the Atlantic, a separate team of researchers had also been trying to unravel the secrets of the new Er blood group, but were beaten by the British team. “That happens in this field,” says Connie Westhoff of the New York Blood Center, who was part of the US research. “We often know that we’re racing to find the solution in several different laboratories.”

She says she and her colleagues have additional blood samples that appear to be from people with a rare Er blood group. And the research may not be over, she suggests—there are possibly more genetic mutations associated with this rare blood to uncover.

“Discovering a new blood group system is like discovering a new planet. It enlarges the landscape of our reality,” says Daniela Hermelin at the Saint Louis University School of Medicine, who was not involved in the study. It adds to our knowledge of how blood incompatibility can affect pregnant mothers and their babies, she explains. And now that cases of blood incompatibility can potentially be attributed to the Er blood group, it increases the chance that doctors can correctly diagnose such a problem and treat it—by giving the baby a blood transfusion in the womb, for example.

It will also be possible to look out for and identify patients who have this troublesome blood. For example, someone might go to a hospital for a transfusion and have a preliminary blood test that reveals the presence of some unusual antibodies. Doctors could send the blood for analysis, and it might turn out that they have the rare Er blood described in the paper. “We have our testing set up to be able to do that,” says Thornton. Rare blood might then be required for that person’s transfusion, she adds. In the future, scientists in a lab might be able to grow red blood cells that could be offered to these patients for transfusion purposes.

It’s very, very unlikely that you’d have an incompatibility with someone else’s blood due to Er antigens, says Avent. But “if you do, it’s something you want to know about.”

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UM School of Medicine Researchers Find Blood Type Linked to Risk of Stroke Before Age 60

August 31, 2022 | Deborah Kotz

Research Could Lead to Potential New Ways to Prevent Strokes in Young Adults

A person’s blood type may be linked to their risk of having an early stroke, according to a new meta-analysis led by University of Maryland School of Medicine (UMSOM) researchers. Findings were published today in the journal Neurology . The meta-analysis included all available data from genetic studies focusing on ischemic strokes, which are caused by a blockage of blood flow to the brain, occurring in younger adults under age 60.

He and his colleagues conducted the study by performing a meta-analysis of 48 studies on genetics and ischemic stroke that included 17,000 stroke patients and nearly 600,000 healthy controls who never had experienced a stroke. They then looked across all collected chromosomes to identify genetic variants associated with a stroke and found a link between early-onset stroke – occurring before age 60 – and the area of the chromosome that includes the gene that determines whether a blood type is A, AB, B, or O.

The study found that people with early stroke were more likely to have blood type A and less likely to have blood type O (the most common blood type) -- compared to people with late stroke and people who never had a stroke. Both early and late stroke were also more likely to have blood type B compared to controls. After adjusting for sex and other factors, researchers found those who had blood type A had a 16 percent higher risk of having an early stroke than people with other blood types. Those who had blood type O had a 12 percent lower risk of having a stroke than people with other blood types.

The researchers emphasized that the increased risk was very modest and that those with type A blood should not worry about having an early-onset stroke or engage in extra screening or medical testing based on this finding.

“We still don’t know why blood type A would confer a higher risk, but it likely has something to do with blood-clotting factors like platelets and cells that line the blood vessels as well as other circulating proteins, all of which play a role in the development of blood clots,” said Dr. Kittner. Previous studies suggest that those with an A blood type have a slightly higher risk of developing blood clots in the legs known as deep vein thrombosis. “We clearly need more follow-up studies to clarify the mechanisms of increased stroke risk,” he added.

In addition to Dr. Kittner and Dr. Mitchell, UMSOM faculty involved in this study included Huichun Xu, MD, PhD , Associate Professor of Medicine; Patrick F. McArdle, PhD , Associate Professor of Medicine; Timothy O’Connor, PhD , Associate Professor of Medicine; James A. Perry, PhD , Assistant Professor of Medicine; Kathleen A. Ryan, MPH, MS, Statistician; John W. Cole, MD , Professor of Neurology; Marc C. Hochberg, MD, MPH , Professor of Medicine; O. Colin Stine, PhD , Professor of Epidemiology and Public Health; and Charles C. Hong, MD, PhD , Melvin Sharoky MD Professor of Medicine

A limitation of the study was the relative lack of diversity among participants. The data was derived from the Early Onset Stroke Consortium, a collaboration of 48 different studies across North America, Europe, Japan, Pakistan, and Australia. About 35 percent of the participants were of non-European ancestry.

“This important and surprising research finding adds to our current knowledge about non-modifiable risk factors for stroke -- including a person’s blood type,” said Mark T. Gladwin, MD , Vice President for Medical Affairs at University of Maryland, Baltimore, and the John Z. and Akiko K. Bowers Distinguished Professor and Dean at UMSOM. “This study also highlights the need for future research to sort out the connection of blood group with clotting risk in more diverse populations. This will help us to better understand the strength of this association across different races and ethnicities.”

The study was supported by the National Institutes of Health and Department of Veterans Affairs. Researchers from more than 50 institutions worldwide were co-authors on this study.

About the University of Maryland School of Medicine

Now in its third century, the University of Maryland School of Medicine was chartered in 1807 as the first public medical school in the United States. It continues today as one of the fastest growing, top-tier biomedical research enterprises in the world -- with 46 academic departments, centers, institutes, and programs, and a faculty of more than 3,000 physicians, scientists, and allied health professionals, including members of the National Academy of Medicine and the National Academy of Sciences, and a distinguished two-time winner of the Albert E. Lasker Award in Medical Research. With an operating budget of more than $1.3 billion, the School of Medicine works closely in partnership with the University of Maryland Medical Center and Medical System to provide research-intensive, academic, and clinically based care for nearly 2 million patients each year. The School of Medicine has nearly $600 million in extramural funding, with most of its academic departments highly ranked among all medical schools in the nation in research funding. As one of the seven professional schools that make up the University of Maryland, Baltimore campus, the School of Medicine has a total population of nearly 9,000 faculty and staff, including 2,500 students, trainees, residents, and fellows. The combined School of Medicine and Medical System (“University of Maryland Medicine”) has an annual budget of over $6 billion and an economic impact of nearly $20 billion on the state and local community. The School of Medicine, which ranks as the 8th highest among public medical schools in research productivity (according to the Association of American Medical Colleges profile) is an innovator in translational medicine, with 606 active patents and 52 start-up companies. In the latest U.S. News & World Report ranking of the Best Medical Schools, published in 2021, the UM School of Medicine is ranked #9 among the 92 public medical schools in the U.S., and in the top 15 percent (#27) of all 192 public and private U.S. medical schools. The School of Medicine works locally, nationally, and globally, with research and treatment facilities in 36 countries around the world. Visit medschool.umaryland.edu

Deborah Kotz Senior Director of Media Relations Office of Public Affairs & Communications University of Maryland School of Medicine Email: [email protected] o: 410-706-4255 c: 410-804-0054 t: @debkotz2

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What Your Blood Type Can Tell You About Your Health

A hematologist and professor of medicine at Tufts University School of Medicine shares what we know, and don’t know, about how blood types affect our risk of certain diseases

Most people don’t think about their blood type unless they need surgery or are planning to donate blood. But we can learn more from our blood types than simply whether or not we can safely accept a transfusion from a donor. Using large, population-wide surveys, researchers have found that certain blood types are associated with greater risks of heart disease, stroke, and certain cancers, says hematologist Raymond Comenzo , a professor at Tufts University School of Medicine and medical director of the Blood Bank and Transfusion Medicine Laboratory at Tufts Medical Center .

“It’s not the kind of work that can guide clinical decision making for a specific patient,” Comenzo says. “But these linkages can provide avenues for further research to better understand these diseases and the risks for various populations.”

There are four major blood types: A, B, AB, and O. Our blood type is based on specific antigens, which are molecules that stimulate an immune response, that are present on the outside of our red blood cells. A person with B blood, for example, has B antigens on their red blood cells. This means that their body will recognize other B antigens as safe and won’t react to them. But if their body encounters A antigens from, say, transfused blood, it will immediately try to destroy those cells as if they were an infection. People with AB blood have both A and B antigens, and people with O blood have neither.

Blood types are genetic; they stem from variations in one gene in our body known as the ABO gene and they’re not something we can change. But learning how they impact different disease risks can improve our understanding of how and why people develop different health issues.

Cancers. Research shows that people with type A blood are at a higher risk of developing certain stomach cancers. Bacterial infections from helicobacter pylori are more common in patients who have type A blood, and these infections can cause stomach ulcers, inflammations, and sometimes lead to cancer, Comenzo says. H. pylori may also be connected to higher rates of pancreatic cancer in blood types A, B, and AB.

These three blood types may influence the risk of other cancers as well. “For patients who have type A, B, or AB blood, the ABO gene can also play a role in heightening the risk of certain cancers, particularly lung, breast, colorectal, and cervical cancers,” Comenzo says. But researchers still aren’t sure exactly how they are connected.

Heart disease . According to the American Heart Association, A, B, and AB blood types are associated with a greater risk of heart attack due to coronary artery disease than type O blood. In particular, people with AB blood appear to have the highest risk. These blood types have also been linked to higher rates of clotting disorders, which is likely related.

Stroke. A recent study found that people with blood type A were slightly more likely to have a stroke before the age of 60 than people with blood type O. More research is needed to determine what might be causing this connection, but the researchers suggest it might have to do with how different blood types contribute to clotting factors.

Mosquitoes and malaria . In lab experiments, mosquitoes seem to prefer feeding on people with type O blood, although other genetic factors also play a part. Fortunately, having type O blood helps protect people from the most severe effects of malaria, a mosquito-borne disease.

COVID-19. In a large study of European patients, analysis suggested that patients with Type O blood were at a slightly lower risk of dying from COVID-19.

“This was data from before we had vaccines, of course,” Comenzo says. “It doesn’t really translate into risk for an individual patient, because the relative risk is so small.”

Understanding how different blood types may contribute to these risks can help improve how we recognize and manage different diseases at a population level. But individual people shouldn’t suddenly start worrying too much about the particular risks associated with their blood type, Comenzo says. Many of these differences in risk are small, and patients concerned about their health should focus on the risk factors that they can control.

“There are plenty of ways that individuals who have these blood types may minimize their risk,” Comenzo says. “And that’s with exercise, a healthy diet, not smoking, and similar lifestyle changes.”

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Why Blood Type Seems to Be Linked With COVID-19 Risk

Since the early months of the COVID-19 pandemic, scientists have investigated whether ABO blood group is related to the risk of SARS-CoV-2 infection and illness.

After all, nearly 20 years ago, researchers reported that type O blood was associated with a lower risk of the original SARS. In addition, other studies had linked type O blood to a higher risk of infection by cholera , norovirus , and Helicobacter pylori .

“It’s probably why we still have ABO blood groups in the population,” with each of them having an advantage, depending on the disease, Sean Stowell, MD, a transfusion specialist at the Brigham and Women’s Hospital and Harvard University in Boston, explained in an interview.

Perhaps not surprisingly, given the earlier SARS observations, Stowell said that most studies of the relationship between SARS-CoV-2 and blood group have found that, all other things being equal, people with type A were more likely to become infected than people with type O. Although some studies have found no relationship between blood type and COVID-19 risk, none has linked type O to a higher risk of SARS-CoV-2 infection.

Why would blood group make any difference to SARS-CoV-2? Several new studies offer possible explanations. One from Stowell and colleagues, recently published in Blood , suggests that having type A blood makes SARS-CoV-2 “stickier” to host cells.

The Backstory

Early in the pandemic, when Stowell was on the faculty at Emory University, the US Centers for Disease Control and Prevention asked him and his colleagues to develop a serology test to check for evidence of SARS-CoV-2 infection.

Their test, which the Food and Drug Administration authorized for emergency use, used a recombinant form of the receptor-binding domain (RBD) region of the SARS-CoV-2 spike protein to detect antibodies in blood specimens. Targeting the RBD seemed to make the most sense “because it was the thing that sticks to cells,” Stowell explained, “which is why we started looking at it more carefully.”

That’s when Stowell’s team noticed something surprising: SARS-CoV-2’s RBD resembled an ancient family of carbohydrate-binding proteins called galectins, present in every animal species. Analysis by Stowell and his collaborators revealed that some galectins shared up to 11% of their nucleotide sequence with the SARS-CoV-2 RBD.

“We were not expecting that at all,” he said.

Some galectins have been shown to engage ABO antigens, which are carbohydrates—sugars, to be precise. Perhaps those antigens were the reason why the SARS-CoV-2 RBD seemed to find blood type A sweeter than blood type O, Stowell and his colleagues speculated.

The Methods

SARS-CoV-2 enters cells through the angiotensin-converting enzyme 2 (ACE2) receptors on their surface. The receptors’ levels vary even among individuals with the same blood type.

So Stowell’s team undertook the painstaking task of engineering Chinese hamster ovary (CHO) cells that expressed both ACE2 and either the blood group A antigen or the blood group O antigen found on epithelial cells, which line the respiratory tract from the nose to the lungs. These antigens differ slightly from those found on red blood cells.

“The virus isn’t trying to infect our blood cells. The virus is trying to infect our lungs,” Stowell explained.

It took a year and a half to engineer the CHO cells. Once the cells were ready, the researchers investigated whether the type of blood group antigen they expressed influenced how well SARS-CoV-2 bound with them. They also compared the binding specificity of the SARS-CoV-2 RBD with that of galectins, specifically the C-terminal of Gal-4 (Gal-4C), which, they’d found, interacted with blood group antigens, and used Gal-1, which did not interact with the antigens, as a control.

What They Learned

Although the CHO cells had identical levels of ACE2 receptors, those that expressed the blood group A antigen were significantly more likely to be infected with SARS-CoV-2 than those that expressed the blood group O antigen.

Incubating the CHO cells with Gal-4C inhibited SARS-CoV-2 infection of cells that expressed blood group A but not blood group O. Because of its similarity to the RBD, Gal-4C had blocked SARS-CoV-2 from binding with cells expressing the A antigen, reducing the ability of those cells to facilitate RBD interactions with their ACE2 receptors.

Incubating Gal-1 with the CHO cells made no difference in SARS-CoV-2 infection of either the A-expressing cells or the O-expressing cells. This was as expected because that particular galectin doesn’t play favorites when it comes to blood group antigens.

Both the Delta and Omicron variants of the virus preferred the blood group A–expressing cells, but Omicron’s proclivity for the A antigen was even stronger.

Although the researchers did not engineer CHO cells that expressed blood group B antigen, an additional analysis found enhanced Delta and Omicron RBD affinity for blood type B compared with blood type O.

“The virus still requires ACE2 to get in [cells],” Stowell pointed out. “The blood group A antigen on the cells just makes the virus a little stickier to the cells.” In other words, he said, having blood group A helps SARS-CoV-2 stick around and locate the ACE2 receptors on cells.

The findings also suggest that galectin-4 might modulate the influence of blood type on SARS-CoV-2 infection, although “galectin expression at sites of infection remains incompletely understood,” the researchers noted in their article.

“Thus,” they wrote, “variations in ACE2 levels, blood group A expression, and many other factors likely influence the overall risk of SARS-CoV-2 infection in a given population.”

Other Possibilities

Other new studies also add to the body of evidence around blood group and SARS-CoV-2 susceptibility and offer different potential mechanisms.

Researchers in China enrolled patients hospitalized with COVID-19—137 with milder disease and 97 who were critically ill. They found that blood type wasn’t related to clinical outcomes, such as acute respiratory distress syndrome or death, but was associated with the likelihood of becoming infected with SARS-CoV-2. Further study showed that among healthy people, those with type A blood had significantly higher ACE2 protein levels than those with other blood types. That could help explain why type A blood was overrepresented among the patients hospitalized with COVID-19. In a laboratory experiment, the researchers found that the rate of SARS-CoV-2 RBD binding to red blood cells was highest among people with type A and lowest in people with type O blood.

A study conducted by Danish researchers recruited 108 staff members at 3 hospitals who did not use personal protective equipment while caring for patients with undiagnosed COVID-19 from April to September 2020. Of the 108 staff unknowingly exposed to SARS-CoV-2, 34 became infected. Blood group O was associated with a lower risk of COVID-19 than blood groups A, B, and AB. High titers of preexisting natural anti-A antibodies, found in people with type O and type B blood, and anti-B antibodies, found in people with type O and type A blood, also were associated with a lower risk of COVID-19.

Researchers in Italy assessed SARS-CoV-2 seroprevalence among 35 709 blood donors. Overall, 6.8% of them were found to be positive for SARS-CoV-2 immunoglobulin G antibodies. But the seroprevalence in donors with type A and type AB blood was 7.5% compared with 6.2% in donors with type O blood. Seroprevalence in donors with type B blood fell in the middle at 6.5%. The authors offered 2 hypotheses to explain their findings: the A antigen present in people with blood type A and AB plays a role in SARS-Cov-2 binding with ACE2 receptors. In addition, anti-A and anti-B antibodies, both of which are produced naturally in people with type O blood, might block the virus from sticking to cells, lowering the risk of infection.

“In my opinion, this paper provides direct evidence that blood group A antigen is a risk factor for SARS-CoV-2,” Xingbin Hu, MD, PhD, a transfusion medicine specialist at Xijing Hospital in Xi’an, Shaanxi, China, said about the study in Blood . “Undoubtedly, the mechanism between blood group antigens and SARS-CoV-2 infection susceptibility still needs further lab and clinical evidence,” Hu, a coauthor of the study of patients hospitalized in China, wrote in an email.

Hu’s team noted that their research shows that blood type A may be a biological marker for susceptibility to SARS-CoV-2 infection and might “provide new ideas for clinical diagnosis, treatment, and prevention of COVID-19.”

Of course, blood type isn’t a modifiable risk factor. Except in rare cases , mainly after receiving stem cells from a donor with a different blood type or developing certain malignancies or infections, blood type remains the same from birth to death.

“I don’t want people to worry,” said Stowell, who himself happens to have type A blood.

Although individuals who don’t have type O blood might be more likely to contract COVID-19, people with blood group O aren’t immune to the disease, Stowell emphasized.

That’s why everyone, no matter their blood type, should take steps to minimize their chances of SARS-CoV-2 infection, he noted, such as being up to date with vaccinations.

Published Online: August 16, 2023. doi:10.1001/jama.2023.15996

Conflict of Interest Disclosures: Dr Stowell reported consulting for Novartis, Cellics, Argenx, and Alexion and receiving speaking honoraria from Grifols. No other disclosures were reported.

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Rubin R. Why Blood Type Seems to Be Linked With COVID-19 Risk. JAMA. 2023;330(9):795–796. doi:10.1001/jama.2023.15996

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What Your Blood Type Can Tell You About Your Health

A lab technician holds a test tube containing a blood sample.

COVID-19. In a large study of European patients, analysis suggested that patients with Type O blood were at a slightly lower risk of dying from COVID-19.

“This was data from before we had vaccines, of course,” Comenzo says. “It doesn’t really translate into risk for an individual patient, because the relative risk is so small.”

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What Your Blood Type Says About Your Health

Knowing your type could give clues to your risk of stroke and heart attack.

doctor with hands around various blood types

Hallie Levine,

Do you know your blood type? There’s a good chance that you don’t. More Americans know their horoscope sign (66 percent) than their blood type (51 percent), according to a survey published this year by medical laboratory company Quest Diagnostics.

There are compelling health reasons why you should know, especially when it comes to your heart. Research suggests that people with certain blood types — namely A and B — are at higher risk to develop blood clots and to have heart attacks and strokes.

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“We think about blood type a lot when we think about transfusions,” says Robert Salazar, M.D., a cardiologist at Memorial Hermann Health System in Houston. There may be some benefits to know about it for heart health , he adds. “Increasingly, there is a push towards the individualization of medicine and medical advice,” he explains. Adding information about blood type, he says, may help inform doctors on how to best treat patients.

Types of blood

Blood type and your health.

What the research shows:

Types A and B

Higher risk of blood clots, heart attacks and strokes.

Higher risk of stroke and inflammation. Those with AB+ blood can accept blood from all donors and are called universal recipients.

Slightly lower risk of thrombosis, blood clots, heart attacks and strokes. People with type O- blood are universal donors and can donate to anyone.

Note that a healthy lifestyle likely trumps blood type in terms of increasing or decreasing risks.

Blood types are determined by the presence or absence of certain substances, called antigens, that can trigger an immune response if they are foreign to the body.

There are four main blood types: A, B, O and AB, according to the American Red Cross . In addition to these antigens, there’s a protein called the Rh factor, which can either be present (+) or absent (-). That means there are eight blood subtypes: A+, A-, B+, B-, O+, O-, AB+, AB-.

Types A and B and blood clots

People with blood types A and B are at higher risk to develop blood clots compared with people who have type O blood, according to a 2020 study published in the American Heart Association journal Arteriosclerosis, Thrombosis, and Vascular Biology . The study, which looked at more than 400,000 people, found that types A and B were 50 percent more likely to develop blood clots in the legs called deep vein thrombosis and 47 percent more likely to develop a pulmonary embolism — when a clot travels to the lungs — than people with type O blood. They were 8 percent more likely to have a heart attack and 10 percent more likely to experience heart failure than type Os.

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Why blood type affects clot risk

There are many possible reasons for why this happens, says Mary Cushman, M.D., a hematologist at the University of Vermont Medical Center and a professor of medicine and pathology at the Larner College of Medicine at UVM in Burlington, Vermont.

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“The enzyme that controls blood type has other actions,” she explains. One of these is to modify a protein called von Willebrand factor, which is very important in forming blood clots . “The modifications to the protein are different in different blood types,” she says. “So people with type O blood have the lowest levels of von Willebrand factor on average and the lowest risk of abnormal clots. Type AB has the highest level and, in some studies, the highest risk of blood clots.”

There may also be some differences in platelets, the small cell fragments in the blood that form clots, says Joshua Beckman, a cardiologist at the UT Southwestern Medical Center. This may make you more susceptible to clotting.

Type A, type AB and cholesterol, stroke

There’s evidence to suggest that type A blood is linked to higher levels of low-density lipoprotein (LDL) cholesterol, the waxy substance that clogs arteries. Type AB blood is linked to inflammation, which may adversely affect blood vessels. Larger studies need to be done before coming to any definite conclusions, Beckman says.

Blood type may impact stroke risk, too. A 2022 study published in the medical journal Neurology reviewed 48 studies of 17,000 stroke patients and found that people with type A were 16 percent more likely to have an early stroke than people with other blood types, and those with type O were 12 percent less likely. An earlier study done by Cushman found that blood type AB, compared with O, had a 1.8 times higher risk of stroke; other blood types weren’t affected.

Blood type and other health risks

Scientists are studying how blood type might affect risks from the COVID-19 virus , but they say it’s too early to draw firm conclusions. Research has linked type O blood with a lower chance of getting seriously ill from cholera, and it may offer some protection from severe malaria.

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What you can do

It’s important to keep research findings in context. Though certain blood types could mean an increased chance of health problems such as blood clots and stroke , the risk is relatively small compared with the dangers of smoking and high blood pressure, and blood type doesn’t tell you much about your personal risk, Cushman points out.

You also shouldn’t let your blood type give you a false sense of security. If you’re having surgery or if you have cancer — both situations that can raise the risk of blood clots — Cushman recommends that you talk to your health care provider about a blood clot prevention plan. “If you have O blood type, you may have slightly lower risk of some diseases like thrombosis, but it doesn’t completely protect you from the risk,” she says. Thrombosis occurs when clots block blood vessels.

Knowing your blood type may give you added insight into your heart health, Salazar says. Though doctors often talk about manageable risk factors, such as high blood pressure, diabetes and smoking, there’s less conversation around genes or the genetic risk for heart disease, he says. Having a patient’s blood type is a “way to try to narrow down individuals who may be at high risk,” he says. For these people, following the American Heart Association’s Life’s Essential 8 — eating right, staying active, not smoking , getting enough sleep, managing weight, controlling cholesterol, managing blood sugar and managing blood pressure — may be even more important.

Regardless of your blood type, everyone should have a heart-healthy lifestyle, Cushman says. “Following the guidance of the American Heart Association’s Life’s Essential 8, for example, will add years to your life and reduce your risk of thrombosis-related outcomes like heart attack, stroke and venous thrombosis,” she says.

How to find out your blood type

A simple blood test can reveal your blood type. If you’re curious, you can ask your doctor to have it tested the next time you need bloodwork. There’s another very quick and easy way to figure out your blood type that’s also altruistic: Give blood.

A 2019 national survey conducted by the Red Cross found that more than half of people believe they need to know their blood type to do so, but that’s not true. Once you give blood, you’ll learn your blood type when you receive your donor card, and you can create a profile through the Red Cross Blood Donor App. Slightly more than a third — 37 percent — of the world’s population has the most frequently occurring blood type, O+.

Editor's note: A previous version of this article displayed accurate information about the AB blood type under the wrong section in a sidebar. The sidebar has been corrected.

Hallie Levine is a contributing writer and an award-winning medical and health reporter. Her work has appeared in The New York Times, Consumer Reports, Real Simple, Health and Time , among other publications.

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How does blood work, and what problems can occur?

The components of blood include plasma, platelets, and red and white blood cells that circulate through the body. Blood supplies essential substances, such as sugars and oxygen, to cells and organs, and removes waste from cells.

Hematologists work to identify and prevent blood and bone marrow diseases. They also study and treat the immune system, blood clotting, and blood vessels.

Health conditions that affect the blood can be life threatening, but effective treatment is often available. In the United States, blood diseases accounted for 10,066 deaths in 2008, mostly different types of anemia.

The main components of blood are:

red blood cells
white blood cells

Plasma accounts for around 55% of blood fluid in humans. Plasma is 92% water, and the contents of the remaining 8% include:

mineral salts

The remaining 45% of blood mainly consists of red and white blood cells and platelets. Each of these has a vital role to play in keeping the blood functioning effectively.

Find out what plasma donation involves.

Red blood cells, or erythrocytes

Red blood cells have a slightly indented, flattened disk shape. They transport oxygen to and from the lungs. Hemoglobin is a protein that contains iron and carries oxygen to its destination. The life span of a red blood cell is 4 months, and the body replaces them regularly. The human body produces around 2 million blood cells every second.

The expected number of red blood cells in a single drop (microliter) of blood is 4.5–6.2 million in males and 4.0–5.2 million in females.

What percentage of red blood cells should people have in their body?

White blood cells, or leukocytes

White blood cells make up less than 1% of blood content, forming vital defenses against disease and infection. The number of white blood cells in a microliter of blood usually ranges from 3,700–10,500 . Higher or lower levels of white blood cells can indicate disease.

What does it mean if a person has a high white blood cell count?

Platelets, or thrombocytes

Platelets interact with clotting proteins to prevent or stop bleeding. There should be between 150,000 and 400,000 platelets per microliter of blood.

Bone marrow produces red blood cells, white blood cells, and platelets, and from there they enter the bloodstream. Plasma is mostly water that is absorbed from ingested food and fluid by the intestines. The heart pumps them around the body as blood by way of the blood vessels.

What does it mean if a person has high or low platelet levels?

Blood has various functions that are central to survival. They include:

supplying oxygen to cells and tissues
providing essential nutrients to cells, such as amino acids, fatty acids, and glucose
removing waste materials, such as carbon dioxide, urea, and lactic acid
protecting the body from diseases, infections, and foreign bodies through the action of white blood cells
regulating body temperature

The platelets in blood enable the clotting, or coagulation, of blood. When bleeding occurs, the platelets group together to create a clot. The clot forms a scab, which stops the bleeding and helps protect the wound from infection.

Blood groups

A person’s blood type is determined by the antigens on the red blood cells. Antigens are protein molecules on the surface of these cells.

Antibodies are proteins in plasma that alert the immune system to the presence of potentially harmful foreign substances. The immune system protects the body from the threat of disease or infection.

Knowing a person’s blood type is essential if they are receiving an organ donation or blood transfusion. Antibodies will attack new blood cells if the blood is the wrong type, leading to life threatening complications. For example, anti-A antibodies will attack cells that have A antigens.

Red blood cells sometimes contain another antigen called RhD. Doctors also note this as part of the blood group. A positive blood group means that RhD is present.

Humans can have one of four main blood groups. Each of these groups can be Rhd-positive or -negative, forming eight main categories.

Group A positive or A negative: A antigens are present on the surfaces of blood cells. Anti-B antibodies are present in the plasma.
Group B positive or B negative: B antigens are present on the surfaces of blood cells. Anti-A antibodies are present in the plasma.
Group AB positive or AB negative: A and B antigens are present on the surfaces of blood cells. There are no antibodies in the plasma.
Group O positive and O negative: There are no antigens on the surfaces of blood cells. Both anti-B and anti-A antibodies are present in the plasma.

People with group O blood can donate to virtually any blood type, and people with group AB+ blood can usually receive blood from any group.

People can talk with their doctor to find out their blood type or find out by donating blood.

Blood groups are important during pregnancy. If a pregnant person has RhD-negative blood, for example, but the fetus inherits RhD-positive blood, treatment will be necessary to prevent a condition known as hemolytic disease of the newborn.

Learn more about blood types in general and rare blood types .

Disorders and diseases of the blood can impair the many functions that blood performs.

Some common blood disorders are:

Anemia : This happens when low red blood cell or hemoglobin levels mean the cells do not transport oxygen effectively, leading to fatigue , pale skin, and other symptoms.
Blood clotting : Clotting helps wounds and injuries heal, but blood clots that form inside a blood vessel can create a blockage, which can be life threatening. If clots become dislodged and move through the heart to the lungs, a pulmonary embolism can form.
Blood cancers : Cancers such as leukemia, myeloma , and lymphoma occur when blood cells start to divide uncontrollably without dying off at the end of their life cycle.
Hemophilia : If a person has low levels of clotting factors in the blood, they can bruise or bleed very easily. They may bleed for too long after a minor injury or surgery, or during menstruation. It affects around 18,000 people in the U.S.
Sickle cell disease : An inherited trait causes red blood cells to take on a crescent shape. It affects over 100,000 people in the U.S., mostly Black Americans. It can severely impact how blood functions and can be life threatening.
Thalassemia : This is also a type of inherited anemia in which the body produces an unusual form of hemoglobin. It affected around 1,000 people in the U.S. in 2008 and is most common in people from around the Mediterranean and parts of Asia.

If symptoms suggest a person may have a blood disorder, they should seek medical advice. A doctor may refer them to a specialist in blood disorders, known as a hematologist.

Learn more here about different blood disorders.

Blood is essential for maintaining the health and life of the human body. It has many functions, including delivering nutrients and oxygen. The four main components of blood are red blood cells, white blood cells, plasma, and platelets.

Problems that arise due to illness or blood loss can be life threatening, but effective treatment is available for many blood-related disorders.

Last medically reviewed on July 14, 2021

Blood / Hematology

How we reviewed this article:

Anemia. (2016). https://www.nhlbi.nih.gov/health-topics/anemia
Bleeding disorders. (2019). https://www.nhlbi.nih.gov/health-topics/bleeding-disorders
Blood basics. (n.d.). https://www.hematology.org/education/patients/blood-basics
Blood cancers. (n.d.). http://www.hematology.org/Patients/Cancers/
Blood clots. (n.d.). http://www.hematology.org/Patients/Clots/
Blood components (n.d.). http://www.redcrossblood.org/learn-about-blood/blood-components
Blood groups. (2020). https://www.nhs.uk/conditions/blood-groups/
Higgins, J. M. (2015). Red blood cell population dynamics. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4717490/
Morbidity and mortality: 2012 chartbook on cardiovascular, lung, and blood diseases. (2012). https://www.nhlbi.nih.gov/files/docs/research/2012_ChartBook_508.pdf
Rapid result test on track to transform sickle cell disease screening for millions. (2019). https://www.nhlbi.nih.gov/news/2019/rapid-result-test-track-transform-sickle-cell-disease-screening-millions
Rh-incompatibility. (n.d.). https://www.nhlbi.nih.gov/health-topics/rh-incompatibility
The complete blood count: A guide for patients with cancer. (2018). https://uihc.org/health-library/complete-blood-count-guide-patients-cancer

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Know Your Blood Type Facts

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Know your blood type, who can receive my blood type

Knowing your blood type is just the beginning. Each blood type has its own unique ways that it can help patients. Think of it like having your own superpower: Knowing your blood type and how it can be best used means you can help even more people. Keep reading for a list of five facts about each blood type that can empower you to help save lives.

TYPE A BLOOD:

Only 1 in 16 people have type A negative blood. This means that A negative blood can be donated to anyone with a blood type of A or AB regardless of the positive or negative.

If you have A negative blood, you can only receive A- or O- blood.

1 in 3 people are type A positive, making it one of the most common blood types.

A positive blood is in high demand because it is present in a large percentage of the population.

Chemotherapy patients have a high demand for platelets from those with A positive blood.

TYPE B BLOOD:

Less than 2% of the population has type B negative blood while about 9% has B positive blood.

B negative red blood cells can be given to both B and AB patients.

B negative patients can only receive blood from other B negative donors or from type O negative donors, who are the universal donors. Both of these types are fairly rare.

B positive red blood cells can be given to both B positive and AB positive patients.

B positive patients can receive blood from B positive, B negative, O positive and O negative donors.

TYPE AB BLOOD:

Less than 1% of the U.S. population has type AB negative blood, making it the least common blood type among Americans.

Patients with AB negative blood type can receive red blood cells from all negative blood types.

Less than 4% of the U.S. population has AB positive blood.

AB positive blood is known as the “universal recipient” because AB positive patients can receive red blood cells from all blood types.

Type AB blood is the only universal plasma donor. This means that type AB plasma transfusions can be given immediately, without losing precious time determining if the patient’s blood type is compatible.

TYPE O BLOOD:

Only 7% of the population has type O negative blood, while 38% has O positive blood, the most common blood type.

O negative is the universal blood type. O positive red blood cells are not universally compatible to all types, but they are compatible to any red blood cells that are positive (A+, B+, O+ and AB+).

Patients with type O negative blood can only receive O negative blood. Similarly, those with O positive blood can only receive transfusions from O positive or O negative blood types.

In major traumas, many hospitals transfuse O positive blood when O negative isn’t available, even when the patient’s blood type is unknown. The risk of reaction is much lower in ongoing blood loss situations and O positive is more available than O negative. Because of their use during emergencies, O blood types are the first to run out during a shortage.

Over 80% of the population has a positive blood type and can receive O positive blood. That’s another reason it’s in such high demand.

With approximately 21 million blood components transfused in the US each year, donors of all blood types are constantly needed. Having an adequate supply of all blood types helps ensure that more patients can get the help they need. If you’re wanting to learn more about blood types, check out this helpful page . You can help keep hospital shelves stocked by scheduling your next appointment to donate today!

Additional Resources

Learn More About Blood and Blood Types

How Blood Donations Help

StarsInsider

This is how your blood type can affect your health

Posted: December 22, 2023 | Last updated: December 21, 2023

<p>In 1930, Dr. Karl Landsteiner won the Nobel Prize for developing the ABO blood group system, the method of classifying blood types. It’s important to know your blood type if you need to receive or <a href="https://www.starsinsider.com/health/466149/the-benefits-of-blood-donation-and-the-celebs-who-support-it" rel="noopener">give blood</a>. A mismatch may cause an immune system reaction that could result in complications such as kidney failure, blood clotting, and, in more extreme cases, death.</p> <p>Fortunately, today’s sophisticated testing techniques have limited these incidents. Nevertheless, research suggests that there are links between blood type and several different diseases. This means that knowing your blood type could also alert you to certain types of diseases, such as multiple sclerosis or diabetes. To find out more about your blood type and its health risks, click through the following gallery.</p><p>You may also like:<a href="https://www.starsinsider.com/n/226683?utm_source=msn.com&utm_medium=display&utm_campaign=referral_description&utm_content=516686v1en-en"> Britain's secret societies</a></p>

In 1930, Dr. Karl Landsteiner won the Nobel Prize for developing the ABO blood group system, the method of classifying blood types. It’s important to know your blood type if you need to receive or give blood . A mismatch may cause an immune system reaction that could result in complications such as kidney failure, blood clotting, and, in more extreme cases, death.

Fortunately, today’s sophisticated testing techniques have limited these incidents. Nevertheless, research suggests that there are links between blood type and several different diseases. This means that knowing your blood type could also alert you to certain types of diseases, such as multiple sclerosis or diabetes. To find out more about your blood type and its health risks, click through the following gallery.

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<p>Like eye color, blood type is passed on genetically from your parents. <a href="https://www.starsinsider.com/health/421818/the-best-ways-to-reduce-your-blood-pressure" rel="noopener">Blood</a> types are determined by the presence or absence of certain antigens, which can trigger an immune response if they're foreign to the body.</p><p><a href="https://www.msn.com/en-us/community/channel/vid-7xx8mnucu55yw63we9va2gwr7uihbxwc68fxqp25x6tg4ftibpra?cvid=94631541bc0f4f89bfd59158d696ad7e">Follow us and access great exclusive content everyday</a></p>

How blood type is determined

Like eye color, blood type is passed on genetically from your parents. Blood types are determined by the presence or absence of certain antigens, which can trigger an immune response if they're foreign to the body.

<p>The ABO blood group system classifies blood types according to the different types of antigens in the red blood cells and antibodies in the plasma. Alongside the RhD antigen status, they determine which blood type will match for a safe transfusion.</p><p>You may also like:<a href="https://www.starsinsider.com/n/232341?utm_source=msn.com&utm_medium=display&utm_campaign=referral_description&utm_content=516686en-us"> Diseases and infections that can kill you within 24 hours</a></p>

ABO and the most common blood types

The ABO blood group system classifies blood types according to the different types of antigens in the red blood cells and antibodies in the plasma. Alongside the RhD antigen status, they determine which blood type will match for a safe transfusion.

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<p>The surface of the red blood cells contains A antigen, and the plasma has anti-B antibody. Anti-B antibody attacks blood cells that contain B antigen.</p><p><a href="https://www.msn.com/en-us/community/channel/vid-7xx8mnucu55yw63we9va2gwr7uihbxwc68fxqp25x6tg4ftibpra?cvid=94631541bc0f4f89bfd59158d696ad7e">Follow us and access great exclusive content everyday</a></p>

The surface of the red blood cells contains A antigen, and the plasma has anti-B antibody. Anti-B antibody attacks blood cells that contain B antigen.

<p>The surface of the red blood cells contains B antigen, and the plasma has anti-A antibody. Anti-A antibody attacks blood cells that contain A antigen.</p><p>You may also like:<a href="https://www.starsinsider.com/n/241394?utm_source=msn.com&utm_medium=display&utm_campaign=referral_description&utm_content=516686en-us"> Serial killers: these are the men who claimed the most lives</a></p>

The surface of the red blood cells contains B antigen, and the plasma has anti-A antibody. Anti-A antibody attacks blood cells that contain A antigen.

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<p>The red blood cells have both A and B antigens, but the plasma doesn't contain anti-A or anti-B antibodies. People with type AB can receive any ABO blood type.</p><p><a href="https://www.msn.com/en-us/community/channel/vid-7xx8mnucu55yw63we9va2gwr7uihbxwc68fxqp25x6tg4ftibpra?cvid=94631541bc0f4f89bfd59158d696ad7e">Follow us and access great exclusive content everyday</a></p>

The red blood cells have both A and B antigens, but the plasma doesn't contain anti-A or anti-B antibodies. People with type AB can receive any ABO blood type.

<p>The plasma contains both anti-A and anti-B antibodies, but the surface of the red blood cells doesn't contain any A or B antigens. Any ABO blood type can receive this type of blood.</p><p>You may also like:<a href="https://www.starsinsider.com/n/250123?utm_source=msn.com&utm_medium=display&utm_campaign=referral_description&utm_content=516686en-us"> Brainy beauty: meet the world's hottest politicians</a></p>

The plasma contains both anti-A and anti-B antibodies, but the surface of the red blood cells doesn't contain any A or B antigens. Any ABO blood type can receive this type of blood.

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<p>Some red blood cells have the Rh factor or antigen. If the red blood cells contain the Rh antigen, they're Rh positive. If they don't, then they're Rh negative.</p><p><a href="https://www.msn.com/en-us/community/channel/vid-7xx8mnucu55yw63we9va2gwr7uihbxwc68fxqp25x6tg4ftibpra?cvid=94631541bc0f4f89bfd59158d696ad7e">Follow us and access great exclusive content everyday</a></p>

Rhesus factor

Some red blood cells have the Rh factor or antigen. If the red blood cells contain the Rh antigen, they're Rh positive. If they don't, then they're Rh negative.

<p>A blood test can determine an individual’s blood type. In a lab, the blood is mixed with three different substances to see how they react. Each substance will contain A or B antibodies, or Rh factor. Observing these reactions will enable the technician to identify a person’s blood type.</p><p>You may also like:<a href="https://www.starsinsider.com/n/268923?utm_source=msn.com&utm_medium=display&utm_campaign=referral_description&utm_content=516686en-us"> Why people keep disappearing from these American national parks</a></p>

Testing for blood type

A blood test can determine an individual’s blood type. In a lab, the blood is mixed with three different substances to see how they react. Each substance will contain A or B antibodies, or Rh factor. Observing these reactions will enable the technician to identify a person’s blood type.

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Heart disease

Research shows that O blood types have a lower risk of coronary heart disease. Experts aren’t sure why. But some believe it might be because other types are likely to have higher cholesterol and higher amounts of a protein that’s linked to clotting.

<p>A small study showed that people with AB blood type are more likely to develop thinking and memory problems, which can lead to dementia, than people with other blood types.</p><p>You may also like:<a href="https://www.starsinsider.com/n/339909?utm_source=msn.com&utm_medium=display&utm_campaign=referral_description&utm_content=516686en-us"> Too cool for school: celebs who never smile on the red carpet</a></p>

A small study showed that people with AB blood type are more likely to develop thinking and memory problems, which can lead to dementia, than people with other blood types.

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<p>Chances are higher you’ll live longer if you have type O blood. Experts believe this is mainly due to a lowered risk of disease in heart and blood vessels.</p><p><a href="https://www.msn.com/en-us/community/channel/vid-7xx8mnucu55yw63we9va2gwr7uihbxwc68fxqp25x6tg4ftibpra?cvid=94631541bc0f4f89bfd59158d696ad7e">Follow us and access great exclusive content everyday</a></p>

Chances are higher you’ll live longer if you have type O blood. Experts believe this is mainly due to a lowered risk of disease in heart and blood vessels.

<p>A, AB, and B blood types are more at risk than type Os, especially people with type A blood. Experts think this might be because of H. pylori, an infection more common with type A blood. It's usually found in the stomach, causing inflammation and ulcers.</p><p>You may also like:<a href="https://www.starsinsider.com/n/439582?utm_source=msn.com&utm_medium=display&utm_campaign=referral_description&utm_content=516686en-us"> The best advice from celebrity makeup artists</a></p>

Stomach cancer

A, AB, and B blood types are more at risk than type Os, especially people with type A blood. Experts think this might be because of H. pylori, an infection more common with type A blood. It's usually found in the stomach, causing inflammation and ulcers.

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<p>Stress increases the body's level of cortisol, also known as the stress hormone. People with type A blood tend to have more cortisol, which can make it harder for them to deal with stress.</p><p><a href="https://www.msn.com/en-us/community/channel/vid-7xx8mnucu55yw63we9va2gwr7uihbxwc68fxqp25x6tg4ftibpra?cvid=94631541bc0f4f89bfd59158d696ad7e">Follow us and access great exclusive content everyday</a></p>

Stress increases the body's level of cortisol, also known as the stress hormone. People with type A blood tend to have more cortisol, which can make it harder for them to deal with stress.

<p>The risk is higher if you're types A, AB, or B. Molecules in types A and B red blood cells help the H. pylori bacteria grow in your gut. This can make you more likely to get pancreatic cancer.</p><p>You may also like:<a href="https://www.starsinsider.com/n/444346?utm_source=msn.com&utm_medium=display&utm_campaign=referral_description&utm_content=516686en-us"> Towering tiaras and more: Extravagant jewelry owned by British royals</a></p>

Pancreatic cancer

The risk is higher if you're types A, AB, or B. Molecules in types A and B red blood cells help the H. pylori bacteria grow in your gut. This can make you more likely to get pancreatic cancer.

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You can get malaria when an infected mosquito bites you. Luckily, if you have blood type O, it's harder for the parasite to attach to the cells.

Peptic ulcers are painful open sores that crop up in the lining of your stomach or upper intestine. They seem to occur more often with blood type O.

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Type 2 diabetes seems to happen more often in people with blood types A and B. However, more research is needed to understand why.

<p>In one study, women with low numbers of healthy eggs were more likely to have type O blood than any other type. However, more research needs to be done to understand why.</p><p>You may also like:<a href="https://www.starsinsider.com/n/461536?utm_source=msn.com&utm_medium=display&utm_campaign=referral_description&utm_content=516686en-us"> Movies that bankrupted their studios</a></p>

In one study, women with low numbers of healthy eggs were more likely to have type O blood than any other type. However, more research needs to be done to understand why.

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Rheumatic disease

Rheumatic disease is a group of more than 200 conditions that cause pain in your joints, connective tissue, tendons, and cartilage. A 2017 study in Turkey showed that some conditions were more common with blood types A and O.

Blood clots

Venous thromboembolism (VTE) is when your blood clots in a deep vein. Research shows that people with types A, B, or AB blood are at a higher risk of VTE.

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You're at greater risk for a stroke if you have blood type AB. Medical professionals think that’s because it’s more likely to clot than other types.

<p>Lupus is an autoimmune disease that causes inflammation and pain throughout the body. Studies have found those with blood types A and B had more severe symptoms than other blood types.</p><p>You may also like:<a href="https://www.starsinsider.com/n/490041?utm_source=msn.com&utm_medium=display&utm_campaign=referral_description&utm_content=516686en-us"> Famous people who became celebrities overnight</a></p>

Lupus is an autoimmune disease that causes inflammation and pain throughout the body. Studies have found those with blood types A and B had more severe symptoms than other blood types.

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<p>MS is a condition when your immune system attacks a protective layer around your nerves called myelin. It's a lifelong condition that can cause serious disability. Research has found that those with blood types A and B have an elevated risk for developing MS.</p><p><a href="https://www.msn.com/en-us/community/channel/vid-7xx8mnucu55yw63we9va2gwr7uihbxwc68fxqp25x6tg4ftibpra?cvid=94631541bc0f4f89bfd59158d696ad7e">Follow us and access great exclusive content everyday</a></p>

Multiple sclerosis (MS)

MS is a condition when your immune system attacks a protective layer around your nerves called myelin. It's a lifelong condition that can cause serious disability. Research has found that those with blood types A and B have an elevated risk for developing MS.

<p>There are two main types of IBD: ulcerative colitis, and Crohn’s disease. Studies both in Italy and South Korea showed that those with blood type O had a lower chance of developing Crohn’s disease.</p><p>You may also like:<a href="https://www.starsinsider.com/n/493882?utm_source=msn.com&utm_medium=display&utm_campaign=referral_description&utm_content=516686en-us"> Celebs who were rejected by other stars</a></p>

Inflammatory bowel disease (IBD)

There are two main types of IBD: ulcerative colitis, and Crohn’s disease. Studies both in Italy and South Korea showed that those with blood type O had a lower chance of developing Crohn’s disease.

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<p>Losing a large quantity of blood is common after severe trauma, such as after a car accident or other injury. Blood type O has been noted to suffer more from hemorrhage-related deaths. But more research needs to be done to understand why.</p><p><a href="https://www.msn.com/en-us/community/channel/vid-7xx8mnucu55yw63we9va2gwr7uihbxwc68fxqp25x6tg4ftibpra?cvid=94631541bc0f4f89bfd59158d696ad7e">Follow us and access great exclusive content everyday</a></p>

Losing a large quantity of blood is common after severe trauma, such as after a car accident or other injury. Blood type O has been noted to suffer more from hemorrhage-related deaths. But more research needs to be done to understand why.

<p>The Rh antigen comes into play during pregnancy, if the mother has Rh-negative blood and her fetus’ blood is Rh-positive. Antibodies from an Rh-negative mother may enter the blood stream of her unborn Rh-positive infant, damaging the red blood cells.</p><p>You may also like:<a href="https://www.starsinsider.com/n/494870?utm_source=msn.com&utm_medium=display&utm_campaign=referral_description&utm_content=516686en-us"> The extravagant spending of royals around the world</a></p>

Risks in pregnancy

The Rh antigen comes into play during pregnancy, if the mother has Rh-negative blood and her fetus’ blood is Rh-positive. Antibodies from an Rh-negative mother may enter the blood stream of her unborn Rh-positive infant, damaging the red blood cells.

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<p>Researchers still don’t understand how blood type and certain diseases are related. It’s thought that genetics and environmental factors both play a role in the development of many conditions. But more research is needed to fully understand this link.</p><p>Sources: (<a href="https://www.medicalnewstoday.com/articles/218285#takeaway" rel="noopener">Medical News Today</a>) (<a href="https://www.webmd.com/a-to-z-guides/ss/slideshow-how-your-blood-type-affects-your-health" rel="noopener">WebMD</a>) (<a href="https://www.healthline.com/health/blood-type-and-autoimmune-diseases#bottom-line" rel="noopener">Healthline</a>)</p><p>See also: <a href="https://www.starsinsider.com/health/499757/health-mistakes-you-didnt-know-youre-making">Health mistakes you didn't know you're making</a></p> <p><a href="https://www.msn.com/en-us/community/channel/vid-7xx8mnucu55yw63we9va2gwr7uihbxwc68fxqp25x6tg4ftibpra?cvid=94631541bc0f4f89bfd59158d696ad7e">Follow us and access great exclusive content everyday</a></p>

The bottom line

Researchers still don’t understand how blood type and certain diseases are related. It’s thought that genetics and environmental factors both play a role in the development of many conditions. But more research is needed to fully understand this link.

Sources: (Medical News Today) (WebMD) (Healthline)

See more: Deadly diseases you thought were gone...but aren't

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World-first research worth bottling

3 April 2024

ADF medical researchers are leading a world-first study to better understand when critically ill patients need a platelet transfusion.

The team recently secured a $1.8 million grant from the Medical Research Future Fund to conduct Australian clinical trials in partnership with the UK’s University of Oxford.

Platelets are tiny blood-cell fragments that clump together to stop bleeding and repair damaged blood vessels.

Patients in intensive care, such as those after major trauma, can have low platelet levels, increasing the risk of bleeding.

Platelet transfusions are commonly given to reduce this risk.

Defence researchers aim to find at what level patients should receive a platelet transfusion so the benefits of the procedure outweigh the risks, such as allergic reaction or effectiveness preventing bleeding in ICU patients.

The team, led by Major Elissa Milford, brings together specialists from across the ADF, including Brigadier Michael Reade and Lieutenant Commander Andrew Flint, in partnership with organisations including Red Cross Lifeblood, the University of Queensland and Monash University.

The study builds on the decade-long Defence research transfusion program, including another clinical trial testing whether frozen platelets would be effective for use in field hospitals.

“It will improve outcomes for patients and ensure the most effective and efficient use of donated platelets – a scarce and expensive resource,” Major Milford said.

“We’re now seeing a return on investment for Defence supporting our clinicians to undertake PhDs.

“Those of us who’ve graduated are now starting to lead our own research programs and train the next generation of researchers, growing the capability.”

The news comes after personnel attended a NATO summit in February to standardise blood transfusion procedures for resuscitating patients.

“Until now there’s been little agreement between countries on how to transfuse blood – everyone has done their own thing,” Brigadier Reade said.

“It’s a big problem if we’re all going to fight together.”

Brigadier Reade, Professor of Military Medicine and Surgery at Joint Health Command and at the University of Queensland, said Defence clinical research positioned Australia as a leader in the field.

“It gives us credibility and a seat at the table, allowing us to influence policy to [our] best advantage,” he said.

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Springer Nature - PMC COVID-19 Collection

Association between ABO blood types and coronavirus disease 2019 (COVID-19), genetic associations, and underlying molecular mechanisms: a literature review of 23 studies

Yujia zhang.

1 Laboratory of Neuro Imaging, USC Stevens Neuroimaging and Informatics Institute, Keck School of Medicine of USC, University of Southern California, 2025 Zonal Ave., Los Angeles, CA 90033 USA

Rachael Garner

Sana salehi.

2 Department of Radiology, Keck School of Medicine of USC, University of Southern California, 1500 San Pablo St., Los Angeles, CA 90033 USA

Marianna La Rocca

Dominique duncan.

An association of various blood types and the 2019 novel coronavirus disease (COVID-19) has been found in a number of publications. The aim of this literature review is to summarize key findings related to ABO blood types and COVID-19 infection rate, symptom presentation, and outcome. Summarized findings include associations between ABO blood type and higher infection susceptibility, intubation duration, and severe outcomes, including death. The literature suggests that blood type O may serve as a protective factor, as individuals with blood type O are found COVID-19 positive at far lower rates. This could suggest that blood type O individuals are less susceptible to infection, or that they are asymptomatic at higher rates and therefore do not seek out testing. We also discuss genetic associations and potential molecular mechanisms that drive the relationship between blood type and COVID-19. Studies have found a strong association between a locus on a specific gene cluster on chromosome three (chr3p21.31) and outcome severity, such as respiratory failure. Cellular models have suggested an explanation for blood type modulation of infection, evidencing that spike protein/Angiotensin-converting enzyme 2 (ACE2)-dependent adhesion to ACE2-expressing cell lines was specifically inhibited by monoclonal or natural human anti-A antibodies, so individuals with non-A blood types, specifically O, or B blood types, which produce anti-A antibodies, may be less susceptible to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection due to the inhibitory effects of anti-A antibodies.

Introduction

Covid-19 pandemic.

The World Health Organization (WHO) received several reports of unidentified pneumonia from Wuhan, China on December 31, 2019. On January 7, 2020, the cause of those reported cases was found to be the 2019 novel coronavirus (2019-nCoV). The disease was later named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and coronavirus disease 2019 (COVID-19). The WHO declared the outbreak a global health emergency on January 30, 2020 [ 1 ].

COVID-19 has become a global concern because it spreads easily and quickly through close contact. The main transmission mechanism is via respiratory droplets containing infectious virus particles. These droplets are transmitted during breathing, coughing, sneezing, and speaking. Airborne transmission and contact transmission are also potential vectors of infection.

Symptoms present following the incubation period, which can be 2–14 days after exposure to the virus. People infected with COVID-19 may have mild to severe symptoms. Common mild symptoms are dry cough, fever, and fatigue. In severe cases, individuals experience acute respiratory distress syndrome, septic shock, or death [ 2 ].

Mortality varies from country to country: currently, the highest mortality is around 8.9% in Mexico, and the lowest is around 0.9% in Turkey [ 3 ]. As of December 21, 2020, there are 77,202,828 cases and 1,639,709 deaths worldwide due to COVID-19 infection [ 3 ]. Managing the spread of this pandemic is very challenging because individuals are contagious during the incubation period [ 2 ]. Moreover, new research has found that 10–30% of people are asymptomatically infected with 2019-nCoV and readily become a conduit for viral transmission [ 4 ].

Defining risk factors

In general, risk factors are variables associated with an increased risk of disease or infection [ 5 ]. There are two types of risk factors: nonmodifiable risk factors and modifiable risk factors [ 6 ]. A conclusive panel of risk factors for COVID-19 infection susceptibility and prognosis is still being explored; however, several risk factors have been proposed.

Nonmodified risk factors for COVID-19 infection are innate traits. Black and Hispanic heritage were found to be risk factors for testing positive for COVID-19, but not for 30-day mortality in a retrospective cohort study of nearly 6 million individuals seeking care from the US Department of Veteran Affairs [ 7 ]. Age over 65 has also been reported as a risk factor for severe outcome, potentially due to increased comorbidities prevalent with age, and decreased efficacy of the immune system, including delayed macrophage function and reduced T cell propagation [ 8 ].

Modifiable risk factors can be controlled, manipulated, or treated through intervention or lifestyle changes. Several meta-analyses have reported that tobacco smokers may be susceptible to increased COVID-19 severity compared with nonsmokers [ 9 – 11 ], including increased Intensive Care Unit (ICU) support, mechanical ventilation, and death [ 12 ]. However, some studies have also reported non-significant relationships between smoking and COVID-19 severity [ 13 ].

Identifying consistent risk factors is critical to ensure that those at higher risk of infection can take added precautions to prevent acquiring the infection. Additionally, understanding those who are at greatest risk for severe prognosis or death may help clinicians better predict patient outcome, allowing for more targeted allocation of limited critical care resources during epidemic surges.

Blood type as a non-modifiable risk factor

ABO blood type is an inherited, non-modifiable trait. Individuals can be A, B, AB, or O depending on the antigens present or absent on erythrocyte surfaces. Blood types may also be characterized as positive or negative depending on the presence of the Rhesus (Rh) factor protein. Numerous studies have previously found associations between ABO blood types and viral respiratory infections such as influenza A (H1N1) and acute respiratory syndrome (SARS) [ 14 – 16 ]. Recently, several studies have proposed relationships between blood types and susceptibility to COVID-19, its significance in the course of the disease, and outcomes [ 17 – 25 ].

Motivations and study aims

The aim of this work is to summarize the key findings of published studies on this topic to identify the relationship between blood type, COVID-19 infection rates, and outcomes, as well as the role of genetics and the underlying molecular mechanism responsible for susceptibility and severity. Although the relationship between blood type, COVID-19 infection, and severe outcome is still under debate, it is critical to understand the potential risk factor’s influence to allow relevant individuals to take added precautions to prevent acquiring the infection.

Methodology

A comprehensive online literature search was conducted using the keywords “COVID-19,” “2019-nCoV,” “SARS-CoV-2,” “ABO blood types,” and “blood group” on PubMed, Embase (Elsevier), and Google Scholar. The identified studies were screened by title and abstracts by two independent reviewers (authors YZ and SS). After discussing the disagreements, the authors reached a consensus to include 23 studies, all published in English, for the final review. The initial data extraction, including study design, number of patients, selection criteria, limitations, and major findings, was carried out by one of the authors (YZ) and assessed for accuracy by other authors (RG, SS, MLR, and DD). We note that this study was primarily designed as a narrative literature review, hence does not entirely follow the Preferred Reporting Items for Systematic Reviews (PRISMA) [ 26 ] method which is designed for systematic reviews/meta-analysis.

Association between ABO blood groups and viral respiratory infections

The role of blood types in bacterial and viral infections has always been an area of interest among researchers in the field [ 27 ]. The association between blood types and different viral respiratory diseases such as H1N1 and severe acute respiratory syndrome (SARS) has been previously discussed in multiple publications [ 14 – 16 ]. SARS, similar to COVID-19, is also caused by a member of Coronaviridae family known as SARS-associated coronavirus (SARS-CoV).

Blood types related to severe acute respiratory syndrome infection

In 2003, several unidentified pneumonia cases were reported in Asia, and later, the illness was confirmed to be caused by a coronavirus named SARS-associated coronavirus (SARS-CoV). This severe respiratory disease was named severe acute respiratory syndrome (SARS). Soon, SARS spread globally, including to North and South America, Europe, and Asia [ 28 ]. Researchers later found an association between blood type and SARS: individuals with blood type O were less likely to become infected with SARS compared with non-blood type O individuals [ 14 ].

Blood types related to influenza infection

Influenza is a common viral infection caused by the influenza virus. Type A and Type B are the two main types of influenza viruses. The flu is a contagious respiratory disease that can cause mild to severe illness, with common symptoms including fever, cough, and sore throat. Flu viruses can be easily spread by droplets that are transmitted when people talk, cough, or sneeze [ 29 ]. Studies have shown an association between flu infection and blood type. During the outbreak of flu caused by H1N1, a subtype of Type A influenza virus, patients with blood group A and B were more susceptible to infection than those with blood group O and AB [ 15 ]. Similarly, researchers found that individuals with blood group B were more susceptible to infection by H3N2, a Type A influenza subtype [ 16 ].

Association between ABO blood type and COVID-19

In order to review evidence of associations between ABO blood types and COVID-19 infection, 23 literature papers were studied. Summarized findings include the associations between blood type and higher infection susceptibility, severe outcomes, and death, as well as genetic association and potential molecular mechanisms that drive the relationship between blood type and COVID-19 infection.

Association of blood type with higher susceptibility of testing positive

Recent studies have shown that blood type A is associated with the highest probability of SARS-CoV-2 infection [ 17 – 21 ]. A summary of findings is reported in Table Table1. 1 . One of the earliest studies in Wuhan, China, suggested that there was an association between blood type A and COVID-19, noting that females with blood type A were more susceptible to infection [ 17 ]. Subsequent studies also reported that blood type A patients had significantly higher odds of acquiring SARS-CoV-2 infection compared with non-A blood types [ 18 – 20 ].

Studies on associations between blood type and higher susceptibility of testing positive for COVID-19

Several studies have also reported that blood type O patients have significantly lower odds of infection, suggesting that blood type O may be a protective factor against infection [ 18 – 20 , 22 , 23 ].

In one multivariate analysis of 14,112 patients who tested positive for COVID-19 in the New York Presbyterian hospital system, investigators reported that blood type A, AB, and B had higher prevalence than blood type O after adjusting for race and ethnicity [ 24 ]. A retrospective study at the First Hospital of Changsha in Changsha, Hunan, China, similarly showed that blood type is a strong risk factor for COVID-19. Blood type O patients had decreased risk of infection compared with non-O blood group patients and blood type A patients had higher risk than all other groups [ 21 ].

While the literature generally agrees that blood type O is a protective factor [ 22 ], there is disagreement on which blood type has the highest susceptibility. Contrary to studies citing blood type A as the most at-risk group, several studies have suggested high risk for blood type B and AB [ 23 ]. One of the largest retrospective cohort studies indicated that risk ratios associated with SARS-CoV-2 infection were 0.87, 1.09, 1.06, and 1.15 for O, A, B, and AB individuals, respectively. Risk ratio compares the risk of health event among one group with another group. If the risk ratio equals to 1, it indicates the identical risk among two groups. A risk ratio is greater than 1, which means the group in the numerator is the exposed group. The risk ratio is smaller than 1; it indicates that the exposed group has lower risk and may play a protective role [ 32 ]. Padhi et al. [ 25 ] also reported that blood type B and AB were associated with higher odds of testing positive for SARS-CoV-2 infection, whereas blood type O was associated with lower odds of testing positive. However, the authors found no correlation between blood type A and positive test rates.

ABO blood type and COVID-19 clinical outcomes of severity

Scientists found that ABO group is associated not only with COVID-19 infection rates but also with severe outcomes, such as requiring mechanical ventilation or death (Table (Table2). 2 ). Literature regarding which blood type is most at risk of severe outcome are more variable than the literature regarding risk of infection.

Summary of findings for ABO blood type and COVID-19 clinical outcomes of severity

For example, blood type O is regarded as a protective factor for infection, but it may not decrease risk of severe outcome. In a study conducted by Zietz et al. [ 24 ], blood type A patients had lower risk of intubation and death compared with blood type O patients, whereas blood type AB had higher risk of intubation and death. Moreover, individuals with blood type B had higher rates of intubation, but lower mortality compared to individuals with blood type O. Conversely, a population-based cohort study conducted in Ontario, Canada, reported that blood type O individuals have lower risk of developing severe conditions or death compared with all other blood types [ 23 ]. Similarly, in a study conducted using Spearman’s rank coefficient analysis on COVID-19 patients collected from the Ministry of Health and Family Welfare in India, scientists found that blood type O was protective against COVID-19 death and that blood type B was more strongly correlated with infection and death [ 25 ].

In contrast, Latz et al. [ 23 ] proposed that blood type A had highest risk of intubation and death. Similarly, a multicenter retrospective analysis showed that patients with blood type A or AB were at higher risk of requiring mechanical ventilation when compared with blood type O or B patients after adjusting for sex, age, and other factors. Blood type A (12% of cohort) and AB patients (32% of cohort) also had higher probability of requiring continuous renal replacement therapy compared with blood type O or B patients after adjusting for sex, age, and other factors. After adjustments, there were no differences in median length of ICU stay or probability of ICU discharge or extubation. There was also no association between blood type and death [ 34 ].

Association of Rhesus factor with susceptibility to COVID-19 infection and outcomes

As blood types can be characterized as positive or negative depending on the presence of the Rhesus (Rh) factor protein, it is also significant for researchers to investigate the association between Rh and COVID-19 infection (Table (Table3 3 ).

Summary of findings for association of Rh with susceptibility to the COVID-19 and outcomes

A study conducted by Latz et al. [ 23 ] reported that Rh(+) was associated with higher odds of testing positive and higher risks of intubation and death. Another study conducted by Zietz et al. [ 24 ] showed that Rh(−) patients had a 2.7% lower risk of initial infection, intubation, and death after adjusting for sex, age, and other demographics. A study conducted by Ray et al. [ 33 ] similarly indicated that individuals with Rh(−) blood type were less susceptible to infection by SARS-CoV-2, especially individuals with O-negative blood type.

However, another hematological study conducted in Sudan proposed that the O-positive blood group has the lowest risk of having severe symptoms, while the authors agreed that A-positive individuals were the most vulnerable when exposed to the virus [ 35 ].

Genetic associations with susceptibility and severity

ABO blood type is determined by the ABO gene, located on the 9 th chromosome. It consists of 7 exons and codes for enzyme glycosyltransferases, which is responsible for the formation of antigens in blood type A and/or B [ 34 ].

In a meta-analysis, investigators sampled 1980 patients with COVID-19-related respiratory failure at seven centers in Italy and Spain and analyzed 8,582,968 single-nucleotide polymorphisms (SNPs). Researchers reported a cross-replicating association with rs11385942 at locus 3p21.31 and with rs657152 at locus 9q34. They found that the 3p21.31 gene cluster is a genetically susceptibility locus in COVID-19 patients with respiratory failure [ 36 ]. Another study conducted by Shelton et al. [ 37 ] using trans-ethnic genome-wide association studies similarly reported a strong association between blood type and COVID-19. In particular, there was strong association at a locus on chr3p21.31 with outcome severity [ 37 ].

Underlying molecular mechanism of susceptibility and severity of ABO blood types

Several researchers have proposed potential molecular mechanisms underlying the susceptibility of particular ABO blood types to COVID-19. A review conducted by Silva-Filho et al. [ 38 ] proposed that the association between ABO blood type and COVID-19 susceptibility and infection progression may be related to the varied distribution of sialic acid-containing receptors on host cells’ surfaces. This distribution is modulated by ABO antigens through carbohydrate-carbohydrate interactions (CCIs), which could maximize or minimize the binding capacity of the virus’s spike protein, the structural glycoprotein that protrudes from the viral envelope, to host cell’s surface receptors. Viral entry is facilitated by interaction of two subunits, S1 and S2. S1 specifically contributes to viral binding to host cell surface receptors via two domains: S1A, corresponding to the N-terminal region, which interacts with sialic-acid containing glycoproteins and glycolipids, and S1B, corresponding to the receptor-binding domain, which binds to Angiotensin-Convertor Enzyme 2 (ACE2) receptors. ACE2 is the central entry route for several coronaviruses into host cells [ 39 ].

ABH antigens are present on the erythrocyte membrane as well as many other cells, including lymphocytes, platelets, and arterial and venular capillary endothelium [ 40 ]. Antigen A especially, but also antigens AB and B, stimulate carbohydrate clustering, whereas H, the antigen characteristic of O blood type, does not induce carbohydrate promotion. Additional carbohydrate clustering facilitates CCIs, maximizing interaction, cell recognition, and aggregation [ 38 , 41 ]. Increased interaction increases the probability of SARS-CoV-2 successfully binding to host cells via specific binding of spike protein domains to ACE2 and CD147, a transmembrane protein that may also facilitate the infectious process via viral anchoring to host cells [ 38 ].

Similar work conducted on SARS-CoV proposed that natural anti-A antibodies may play a role in modulating interaction between the virus and host cells. In the cellular model, spike protein/ACE2-dependent adhesion to ACE2-expressing cell lines was specifically inhibited by monoclonal or natural human anti-A antibodies. Thus, individuals with non-A blood types, specifically O or B blood type, which produce anti-A antibodies, may be less susceptible to SARS-CoV-2 infection due to the inhibitory effects of anti-A antibodies [ 42 ].

Several studies have also suggested that host transmembrane protease serine subtype 2 (TMPRSS2) may play a significant role in ABO group modulation of infection [ 43 , 44 ]. TMPRSS2 is a gene located on human chromosome 21q22.3 [ 45 ], and has been found to be essential for spike protein priming and subsequent infection of SARS-CoV [ 44 ]. However, it has not been confirmed if SARS-CoV and SARS-CoV-2 share identical genomic sequences for the serine protease. Despite this, proteolysis of viral serine by TMPRSS2 may allow for serine mobilization, a key molecule in mucin O-glycan that has been found to be critical for infection [ 44 ]. Following hybridization to yield O- N -acetyl- d -galactosamine (O-GalNAc), SARS-CoV-2 may evade innate or specific immunity by hybridizing ABO blood group, effectively mimicking self-cell presentation. A, B, and AB blood groups have upregulated immunoglobulin M (IgM) activity, while O-group has downregulated IgM activity due to glycosylation. The A, B, and AB blood groups are thus preferential targets because they possess A/B phenotypic-determining enzymes which facilitate greater viral molecular contact, whereas O blood type lacks these enzymes and only binds the virus via hybrid H-type antigen formation. Additionally, IgM downregulation in the O blood group leads to downstream anti-A and anti-B isoagglutinin activity, hallmarks of innate immune activity [ 43 ]. Arend et al. [ 43 ] and Wang et al. [ 46 ] proposed TMPRSS2 inhibition as a potential therapeutic target.

This review examined published empirical papers and meta-analyses related to the relationship between blood type and COVID-19. These studies suggest that blood type may be a risk factor for COVID-19 infection and outcome. Findings related to the highest risk of infection varied among researchers. The majority of researchers report that the greatest risk for susceptibility to COVID-19 infection is among individuals with blood type A, while some others report that individuals with blood type B are the most vulnerable group to infection. Although some researchers report that there is no correlation between blood type and COVID-19 severity or mortality, most studies found that blood types A and AB had higher risk of severe illness or death, while blood type O was protective against death or severe outcomes. Genetic association and several potential mechanisms related to the relationship among blood types A/B, infection susceptibility, and severe outcome were also reported. It has been found that the 3p21.31 gene cluster is a genetically susceptibility locus in COVID-19 patients with respiratory failure. In the cellular model, ACE2 is an entry for virus into host cell. Spike protein/ACE2-dependent adhesion to ACE2-expressing cell lines was specifically inhibited by monoclonal or natural human anti-A antibodies. Thus, in individuals with non-A blood types, specifically O or B blood type, anti-A antibodies may play a protective role in SARS-CoV-2 infection due to its inhibitory effects. Moreover, A, B, and AB blood groups are preferential targets compared to O blood group because they possess A/B phenotypic-determining enzymes which facilitate greater viral molecular contact; however, blood type O lacks these enzymes and only binds the virus via hybrid H-type antigen formation.

This work was supported by the National Science Foundation under Award Number 2027456 (COVID-ARC).

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The authors declare no competing interests.

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EDTA chelates divalent cations which are required for nuclease activity. While the genomic DNA (gDNA) extracted using QIAGEN products , should not have any nuclease activity, it is possible to introduce nucleases during repeated long-term access of the DNA. EDTA helps to prevent any nuclease activity introduced after the genomic DNA extraction procedures.

However, if the gDNA is stored frozen at -20oC or -80oC, nuclease activity is much reduced. It may be possible to leave EDTA out of the storage buffer without negative consequences when samples are kept under these conditions, and when repeated freeze-thaw cycles are avoided.

We do recommend however that gDNA be stored in a neutral to a slightly basic buffered solution (e.g. 10 mM Tris-Cl pH 8.5 to 9.0) to prevent DNA degradation by acid hydrolysis. Note that deionized water mostly has an acidic pH.

Yes, please follow the Supplementary Protocol ' Purification of archive-quality DNA from 10–20 mg fish tissue using the Gentra Puregene Tissue Kit or Gentra Puregene Mouse Tail Kit ' (PG25).

Yes, please follow the Supplementary Protocol ' Scalable purification of archive-quality DNA from 100 to 5 x 10e8 cultured cells using the Gentra Puregene Cell Kit ' (PG09).

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Understanding different blood types
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Blood Types
18.6 Blood Typing
Introduction to Blood Types

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Blood types and timelines 🤔
Physiology Chapter 31 Blood part 6 ( فسلجة تقويمي )
types of blood
O-Positive: The Most Common Blood Type
The Mystery of Blood Types: An Evolutionary Tale
HAEMATOLOGY LECTURE 1

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The Mystery of Human Blood Types
The ABO blood group evolved at least 20 million years ago, but scientists still don't understand the purpose of blood types. Blood banks run blood type tests before blood is sent to hospitals ...
Human ABO Blood Groups and Their Associations with Different Diseases
Human ABO blood type antigens exhibit alternative phenotypes and genetically derived glycoconjugate structures that are located on the red cell surface which play an active role in the cells' physiology and pathology. ... A research in Iraqi persons indicated greater blood glucose, total cholesterol, and blood pressure in blood type O persons, ...
A new understanding of how your blood type influences your health
IN 2023, a paper was published in the journal Blood that ended a mystery stretching back four decades. It detailed the existence of a new blood type, first proposed in the 1980s - and of which ...
Blood Type Biochemistry and Human Disease
Associations between blood type and disease have been studied since the early 1900s when researchers determined that antibodies and antigens are inherited. In the 1950s, the chemical identification of the carbohydrate structure of surface antigens led to the understanding of biosynthetic pathways. The blood type is defined by oligosaccharide ...
Genetically Determined ABO Blood Group and its Associations With Health
Earlier research has associated blood group A with higher total cholesterol levels as well as low-density lipoprotein cholesterol compared with both blood groups B and O. 29 However, ... The association between ABO blood types and venous thromboembolism in individuals with a positive antiphospholipid profile is varied by sex. Lupus. 2018; ...
A Brief History of Human Blood Groups
In a compilation by Mourant in 1958 , referring to a limited and small sampling from Iran (Tehran) by A.Ajir was seen, but there was no systematic and comprehensive research about types and frequencies of blood groups, serum proteins, and red blood cell enzymes, found in Iran.
Blood Types: Main Groups, Most Common, and Rarest
The ABO system has four major blood types: A, B, AB, and O. Blood types are further categorized by the presence (positive or +) or absence (negative or -) of the Rh (D) antigen on the surface of their red blood cells, also known as the Rh factor. This produces the eight major blood types. The Eight Main Blood Types. A+.
Scientists Have Discovered a New Set of Blood Groups
On average, one new blood classification system has been described by researchers each year during the past decade. These newer systems tend to involve blood types that are mind-bogglingly rare ...
UM School of Medicine Researchers Find Blood Type Linked to Risk of
Research Could Lead to Potential New Ways to Prevent Strokes in Young Adults . A person's blood type may be linked to their risk of having an early stroke, according to a new meta-analysis led by University of Maryland School of Medicine (UMSOM) researchers. Findings were published today in the journal Neurology.The meta-analysis included all available data from genetic studies focusing on ...
Karl Landsteiner—Discoverer of the Major Human Blood Groups
Karl Landsteiner first published his seminal discovery about blood types as a footnote in a paper on pathologic anatomy in which he described the agglutination that may occur when the blood of one person is brought into contact with that of another. Others had demonstrated differences among various animals, but in the paper with the famous footnote, Landsteiner noted physiologic differences ...
What Your Blood Type Can Tell You About Your Health
Research shows that people with type A blood are at a higher risk of developing certain stomach cancers. Bacterial infections from helicobacter pylori are more common in patients who have type A blood, and these infections can cause stomach ulcers, inflammations, and sometimes lead to cancer, Comenzo says.
Why Blood Type Seems to Be Linked With COVID-19 Risk
After all, nearly 20 years ago, researchers reported that type O blood was associated with a lower risk of the original SARS. In addition, other studies had linked type O blood to a higher risk of infection by cholera, norovirus, and Helicobacter pylori. "It's probably why we still have ABO blood groups in the population," with each of them having an advantage, depending on the disease ...
Does Your Blood Type Impact Your Diet?
2. Research shows blood type doesn't matter. Studies show that if you eat the diets recommended for blood types A, AB and O, you'll get a positive outcome no matter your blood type, says Peart ...
Blood Types: What They Are and Mean for Your Health
There are four main blood types: A, B, AB and O. Blood bank specialists determine your blood type based on whether you have antigen A or B on your red blood cells. They also look for a protein called the Rh factor. They classify your blood type as positive (+) if you have this protein and negative (-) if you don't.
What Your Blood Type Can Tell You About Your Health
Stroke. A recent study found that people with blood type A were slightly more likely to have a stroke before the age of 60 than people with blood type O. More research is needed to determine what might be causing this connection, but the researchers suggest it might have to do with how different blood types contribute to clotting factors.
Blood Types
Based on the type of antigen, your blood will be categorized as Type A, Type B, Type AB, or Type O. "When antigens come into contact with substances that are unfamiliar to your body, such as certain bacteria, they trigger a response from your immune system. The same type of response can occur during a blood transfusion if your donor's blood ...
What Does Your Blood Type Mean for Your Health?
Research suggests that people with: Type A blood may be at higher risk for COVID-19 infection. Type O blood may be somewhat less likely to test positive for COVID-19 and have less severe disease than people with other blood types. Negative blood types may be also slightly less prone to COVID-19 infection. More data is still needed to confirm ...
Blood Types Explained
Download Guide. There are four major blood groups determined by the presence or absence of two antigens, A and B, on the surface of red blood cells. In addition to the A and B antigens, there is a protein called the Rh factor, which can be either present (+) or absent (-), creating the 8 most common blood types ( A+, A- , B+, B- , O+, O ...
Relationship between blood type and outcomes following COVID-19
2.1. Data supporting blood type correlation with severity of illness. Ray et al published the largest study to date in Canada, investigating the association of blood type with COVID-19. This population-based cohort study from Ontario included a total of 225,556 patients who underwent polymerase chain reaction testing for SARS-CoV-2.
What Your Blood Type Can Mean for Your Health
Blood Type and Your Health. What the research shows: Types A and B. Higher risk of blood clots, heart attacks and strokes. Type AB. Higher risk of stroke and inflammation. Those with AB+ blood can accept blood from all donors and are called universal recipients. Type O. Slightly lower risk of thrombosis, blood clots, heart attacks and strokes.
Blood: Components, functions, groups, and disorders
A person's blood type is determined by the antigens on the red blood cells. Antigens are protein molecules on the surface of these cells. ... academic research institutions, and medical journals ...
Blood Type and Health
Stomach Cancer. 2 /12. A, AB, and B blood types are more at risk than type Os. Specifically, people with type A blood are more likely to get stomach cancer. Researchers think this might be because ...
Facts About Blood Types
TYPE A BLOOD: Only 1 in 16 people have type A negative blood. This means that A negative blood can be donated to anyone with a blood type of A or AB regardless of the positive or negative. If you have A negative blood, you can only receive A- or O- blood. 1 in 3 people are type A positive, making it one of the most common blood types.
This is how your blood type can affect your health
Research shows that O blood types have a lower risk of coronary heart disease. Experts aren't sure why. But some believe it might be because other types are likely to have higher cholesterol and ...
World-first research worth bottling
The team recently secured a $1.8 million grant from the Medical Research Future Fund to conduct Australian clinical trials in partnership with the UK's University of Oxford. Platelets are tiny blood-cell fragments that clump together to stop bleeding and repair damaged blood vessels.
Association between ABO blood types and coronavirus disease 2019 (COVID
The role of blood types in bacterial and viral infections has always been an area of interest among researchers in the field . The association between blood types and different viral respiratory diseases such as H1N1 and severe acute respiratory syndrome (SARS) has been previously discussed in multiple publications [14-16]. SARS, similar to ...
Research Updates, Spring 2024
People with type 2 diabetes who underwent bariatric surgery achieved better long-term blood glucose control compared to people who received medical management plus lifestyle interventions, according to a new study supported by NIDDK.In this large, pooled follow-up study, participants who underwent bariatric surgery, also called metabolic or weight-loss surgery, were also more likely to stop ...
Puregene Kits
Puregene Kits enable purification of high-molecular-weight (100-200 kb) DNA suitable for archiving. The scalable purification procedure gently removes contaminants and inhibitors and allows samples to be purified for use as long-term references.

The Mystery of Human Blood Types

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What Your Blood Type Says About Your Health

Types of blood

Types A and B and blood clots

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Type A, type AB and cholesterol, stroke

Blood type and other health risks

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How to find out your blood type

How does blood work, and what problems can occur?

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This is how your blood type can affect your health

How blood type is determined

ABO and the most common blood types

Rhesus factor

Testing for blood type

Heart disease

Stomach cancer

Pancreatic cancer

Rheumatic disease

Blood clots

Multiple sclerosis (MS)

Inflammatory bowel disease (IBD)

Risks in pregnancy

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