Transfusion of ABO-mismatched platelets leads to early platelet refractoriness

Summary. Forty‐three consecutive patients previously unexposed to platelets and undergoing treatment for acute leukaemia or autografting for relapsed Hodgkin's lymphoma were randomized to receive transfused platelets of either their own ABO group (OG) or of a major mismatched group (MMG). The 26 evaluable patients were equally distributed between the two study groups. Nine of 13 (69%) MMG patients became refractory with a median onset at transfusion 7 (15 d), compared with only one of 13 (8%) OG patients ( P =0.001). Refractoriness was associated with the formation of high titre isoagglutinins, anti‐HLA and platelet specific antibodies. In one patient refractoriness appeared to be due to high titre isoagglutinins alone. Six other patients developed an increase in isoagglutinin titre sufficient to adversely affect platelet increments. Patients receiving ABO‐mismatched platelets had a higher incidence of anti‐HLA antibodies (5 v. 1) and platelet specific antibodies (4 v. 1). ABO‐mismatched platelets transfused prior to the onset of refractoriness resulted in increments similar to those achieved by ABO‐matched platelets. The study demonstrates that ABO‐mismatched platelets are as effective as matched platelets in patients with low titre isoagglutinins requiring only few transfusions. However, the greater incidence of early refractoriness induced in MMG patients indicates that ABO‐mismatched platelets should not be given to patients with marrow failure requiring long‐term support.