ABO blood group

ABO blood group,

a system for classifying human blood on the basis of antigenic components of red blood cells and their corresponding antibodies. The ABO blood group is identified by the presence or absence of two different antigens, A and B, on the surface of the red blood cell. The four blood types in this grouping, A, B, AB, and O, are determined by and named for these antigens. Type AB indicates the presence of both antigens; type O, the absence of both. Corresponding antibodies, anti-A and anti-B agglutinins, can be found in the plasma of type O blood. The plasma components of type A and type B blood are, respectively, devoid of anti-A and anti-B agglutinins; both agglutinins are absent from type AB blood plasma. In addition to its significant role in transfusion therapy and transplantation, the ABO blood grouping contributes to forensic medicine, to genetics, and, with the less important blood groups, to anthropology and legal medicine. See also blood group, Rh factor, transfusion.