Delayed hemolytic transfusion reaction with four antibodies undetected by pretransfusion tests

A case of delayed hemolytic transfusion reaction in a 43-year-old patient is presented. Pretransfusion tests revealed no antibody, but tests performed when the reaction occurred demonstrated four. Ten months and 15 months later, when the patient's serum was again tested, the antibodies were undetectable. The significance of such antibodies is discussed.