ABO system

Refers to a specific antigen system located on red blood cells (RBCs) and platelets (e.g. blood type A, B, AB or O). ABO blood type determination is an essential part of pre-transfusion testing for patients. (Note: Patients with type A RBCs will have type B antibody in their plasma, while patients with type B RBCs will have type A antibody in their plasma. Since type O patient's red blood cells lack A and B antigens, then not surprisingly they could have antibodies to both A and B antigens in their plasma. On the other hand, AB patients plasma is typically devoid of antibodies to either A or B antigen. Hence, the universal donor for RBCs is type O (devoid of A or B antigens) and universal donor for plasma is type AB (devoid of anti-A or Anti-B anti antibodies).