Predictive value of cross‐matching for transfusion of platelet concentrates to alloimmunized recipients

Compatibility tests in which donor platelets were tested with recipient sera were performed retroactively after 64 transfusions of platelets from 59 unrelated donors to 10 alloimmunized patients. Techniques used were serotonin release, aggregometry, platelet factor 3 release, and lymphocytotoxicity, each of which has been advocated as a means of testing donor‐recipient platelet compatibility. Although “false positive” reactions were few (positive crossmatch but satisfactory transfusion response), “false negative” reactions (negative crossmatch but poor transfusion response) were unacceptably high (43% by lymphocytotoxicity, 60% by serotonin release, 76% by platelet factor 3 release, and 83% by aggregometry). We conclude that current methods of detecting isosensitization to platelet alloantigens are less satisfactory than HLA phenotyping in selecting unrelated platelet donors for an alloimmunized patient population.