The ABO blood group is based on the presence (or absence) of two major antigens on red blood cell membranesΓÇöantigen A and antigen B. A person's erythrocytes contain one of four antigen combinations as a result of inheritance: only A, only B, both A and B, or neither A nor B.
A person with only antigen A has type A blood. A person with only antigen B has type B blood. An individual with both antigen A and B has type AB blood. A person with neither antigen A nor B has type O blood. Thus, all humans have one of four possible ABO blood typesΓÇöA, B, AB, or O.
