ABO is the most important blood group system in transfusion medicine. This is because individuals older than 4–6 months of age have naturally occurring antibodies directed against non-self A or B antigens. These antibodies are dangerous, as they activate complement upon binding the corresponding red cell antigen, which then leads to intravascular hemolysis. Pre-transfusion testing always includes obtaining the patient’s ABO type, and then issuing red cells that will not bind the patient’s ABO antibodies. With plasma transfusion, patients will tolerate some amount of incompatible plasma, particularly if the isoagglutinin titer is low. This fact supports development of a policy for ABO out-of-group platelet transfusion that helps to ensure an adequate platelet supply.
KeywordsABO blood group Isoagglutinin ABO compatibility
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