What Is the Rarest Blood Type? Testing, Compatibility, and More

Medically Reviewed By Megan Soliman, MD
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The rarest blood type in the United States is AB negative (AB-). Having a rare blood type affects who you can donate blood to and the types of blood you can receive during a transfusion. Your parents’ blood types determine your blood type. Blood types are classified by the ABO system and Rh factor. The Rh factor determines whether your blood type is positive or negative.

This article explains blood type prevalence, inheritance, and compatibility for donations and transfusions. It also discusses testing to determine your blood type.

What is the rarest blood type?

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AB- is the rarest blood type in the U.S. According to the American Red Cross, only around 0.4% of the US population has type AB- blood.

How are blood types classified?

Blood types are classified into four main groups by the ABO system: A, B, O, and AB.

These blood types are determined by the presence or absence of A and B antigens on the surface of the red blood cells. For example, people with blood type A have the A antigen on their red blood cells. Likewise, people with blood type B have the B antigen on their red blood cells.

People with AB blood have both antigens on their red blood cells. Neither antigen is present on the red blood cells of people with type O blood.

Learn more about blood types.

Another factor in blood type is the Rh factor, which is a protein on red blood cells. If you have Rh factor on your red blood cells, that means you have a positive (+) blood type. For instance, a person with the A antigen and Rh factor on their red blood cells has A+ blood.

Learn more about the Rh factor.

What determines your blood type?

Your blood type is inherited, meaning it is determined by the blood types of your parents.

The ABO types pass down in an autosomal codominant pattern. This means each parent passes down an allele, or a version of a gene, to their child. Also, each allele is equally expressed.

The A and B alleles are codominant. This means they will each influence the blood type of the child equally. The O allele is recessive, meaning that it will only be expressed if there is another copy of the same allele.

How does your blood type affect blood transfusions?

Your blood type affects who you can donate blood to and what kind of blood you can receive during a transfusion. In general, the antigens in the donated blood need to match the antigens in the blood of the recipient.

For example, a person with A blood, blood that contains the A antigen, cannot receive B blood during a transfusion. A person with AB blood can receive blood from a person with A, B, or AB type blood. This is because they have both the A and B antigens.

The Rh factor also matters in blood transfusions. People with Rh-positive blood can receive either Rh-positive or Rh-negative blood. However, people who have Rh-negative blood can only receive Rh-negative blood.

People with type O blood are known as “universal donors.” This means that their blood can be given to people with any blood type.

Blood compatibility

According to the Centers for Disease Control and Prevention, donated blood is tested for ABO blood type and Rh factor before being used in a transfusion. This helps ensure that the person in need of blood is compatible with the blood unit.

If a person receives blood that is incompatible with their blood type, their body can “reject” the blood. The immune system’s antibodies will target the incompatible antigens, causing a range of reactions that can be mild or severe.

Common signs of an adverse reaction to a blood transfusion include:

More serious reaction symptoms can include:

How can you determine your blood type?

A blood typing test can tell you which blood type you have. Ask your doctor about giving a blood sample to determine your type.

Knowing your blood type can help in emergencies where transfusions may be necessary.

Other frequently asked questions

These are a few other common questions about blood types. Megan Soliman, M.D., has reviewed the answers.

What are the 3 rarest blood types?

The American Red Cross lists the three rarest blood types in the U.S. as AB-, B-, and A-.

Is being O+ rare?

O+ blood is the most common blood type in the U.S. Around 44% of the population has O+ blood.

Who has golden blood?

“Golden blood” is another name for the Rhnull blood type. This is a rare blood type occurring in approximately 1 in 6 million people. Rh antigens are completely absent from the red blood cells of people with this blood type. People with golden blood have hemolytic anemia, meaning red blood cells cannot be made fast enough in the body.


The rarest blood type in the U.S. is AB-. Your blood type affects who you can donate blood to and what types of blood you can receive during a transfusion.

Contact your doctor to determine your blood type and compatibility for donations and transfusions.

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Medical Reviewer: Megan Soliman, MD
Last Review Date: 2022 Nov 15
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