AB Blood Type

AB blood type is one of the four types in the ABO blood group system that classifies human blood. In a person with AB type, the surface of red blood cells carries both the A and B antigens. An antigen is a molecule on the surface of a cell that the body's immune system recognizes as either self or foreign.

Because both antigens are present, a person with AB blood typically has no antibodies against A or B blood. For this reason, when considering only the ABO system, an AB person can receive blood from types A, B, AB, and O. This is the origin of the term 'universal recipient'. However, other systems such as Rh (RhD) and other minor antigens must be considered before transfusion.

Inheritance and Detection

The ABO type depends on genes located on chromosome 9. There are three gene variants: A, B, and O. A and B are codominant, while O is recessive. A person with AB type inherited one A gene from one parent and one B gene from the other. This makes AB the rarest type in most world populations.

Rh Classification

The ABO type is usually recorded with RhD status, producing AB-positive (AB+) and AB-negative (AB−). AB-negative is one of the rarest blood types found in blood banks. An AB+ person can receive blood from any ABO and Rh type, but only when no other antibodies are present.

Plasma and Donation

Although an AB person is a universal recipient of red cells, their red cells can be given only to another AB person, because both antigens are present. Conversely, AB plasma typically contains no ABO antibodies, so it can be used for patients of different types. For this reason, some blood banks encourage AB donors to give plasma.