What to Know About Your Blood Type

By Nancy LeBrun 

 Medically reviewed by Anju Goel, MD

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.1

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.2

Rare

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:1

• 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:3

• 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 Rhnull. 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.4

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.5

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.6 One study found people with blood group A have a higher likelihood of infection with COVID-19 than those in blood group O.7

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.8

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.9

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.10

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.11

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.10

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.12 They are generally accurate if performed correctly. Saliva tests are another option, but they may be more costly and less accurate.13

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.

Summary

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.

 Sources

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.

Stanford Blood Center. Blood types.

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
In addition to her extensive health and wellness writing, Nancy has written about many general interest topics for publications as diverse as Newsweek, Teen Vogue, abcnews.com, and Craftsmanship Quarterly. She has authored a book about documentary filmmaking, a screenplay about a lost civil rights hero, and ghostwritten several memoirs.