Blood Type Genetics and Compatibility

There are four main blood types: A, AB, B and O. AB positive is considered the universal recipient, and O negative is considered the universal donor.

Blood Type Frequency (U.S. population)

• O Positive blood – 37%
• O Negative blood  – 7%
• A Positive blood  – 36%
• A Negative blood – 6%
• B Positive blood – 8%
• B Negative blood – 2%
• AB Positive blood – 3%
• AB Negative blood​  – 1%

Blood Type Compatibility

Your ABO blood type is based on the presence or absence of the A and B antigens on your red blood cells. The A blood type has only the A antigen and the B blood type has only the B antigen. The AB blood type has both A and B antigens, and the O blood type has neither A nor B antigen.

By the time you are six months old, you naturally develop antibodies against the antigens your red blood cells lack. For instance, a person with A blood type will have anti-B antibodies, and a person with B blood type will have anti-A antibodies.  If you have type A blood, you cannot receive B blood because your body's anti-B antibodies will fight the B blood's B antigens. It is crucial we have all blood types available to our patients.

Blood Inheritance

ABO Blood Type

Everyone has an ABO blood type (A, B, AB, or O) and an Rh factor (positive or negative). Just like eye or hair color, our blood type is inherited from our parents.

Each biological parent donates one of two ABO genes to their child.  The A and B genes are dominant and the O gene is recessive. For example, if an O gene is paired with an A gene, the blood type will be A.

For instance, a parent with O blood with 2 O genes and a parent with A blood with 2 A genes will have an A blood type child with one A gene and one O gene. 

• AA = A blood type
• AO = A blood type
• BB = B blood type
• BO = B blood type
• OO = O blood type
• AB = AB blood type

Rh Factor

The Rh factor is simply a protein that is found on the covering of the red blood cells. If your red blood cells have this protein, you are Rh positive. If your blood cells don't have this protein, you are Rh negative.

Just as everyone inherits ABO genes, every person inherits one Rh factor gene from each parent. The Rh-positive gene is the dominant gene when paired with an Rh-negative gene.

• Neg/Neg = Negative Rh factor
• Neg/Pos = Postive Rh factor
• Pos/Pos = Positive Rh factor