Delayed haemolytic transfusion reaction due to anti-M antibody.

A female patient with delayed haemolytic transfusion reaction due to anti-M antibody is described. Diagnosis was based on laboratory evidence of haemolysis and on characteristic serological findings. Anti-M was detected in the recipient's serum 7 d after the last transfusion episode. This alloantibody had not been present in the pretransfusion serum. In addition, the direct antiglobulin test was positive on post-transfusion testing and the implicated antibody was eluted from post-transfused red cells. Delayed haemolytic transfusion reactions have long been recognized as a potential hazard of transfusion therapy, but such cases due to anti-M are extremely rare.