A 52-year-old gravida 1, para 1 woman with M- red cells experienced a delayed hemolytic transfusion reaction and exhibited an anti-M antibody following the infusion of four units of M+ red cells. Measurements of erythrocyte survival using 51Cr-labeled donor M+ and M- red cells and in vitro studies of monocyte-macrophage phagocytosis of sensitized reagent red cells implicate anti-M in the pathogenesis of hemolysis.

Delayed hemolytic transfusion reactions usually occur as a result of a secondary immune response with maximal hemolysis occurring seven days posttransfusion. We report a delayed hemolytic transfusion reaction in which hemoglobinuria, anemia, and reticulocytosis developed four weeks after transfusion. The incriminated antibody, anti-C, was first detected eight weeks posttransfusion using enzyme-treated red blood cells. We conclude, that in all likelihood, this hemolytic transfusion reaction was due to a primary immune response, this case illustrates the importance of sequential testing in cases of suspected transfusion reactions.