Platelet support in polysensitized patients: role of HLA specificities and crossmatch testing for donor selection.

Twenty-four thrombocytopenic patients refractory to random-donor platelet support were given 1 06 platelet transfusions obtamed from 57 different HLA-typed single donors. For critical evaluation of the transfusion responses, “fullhouse” HLA typing of donors and a precise measurement of the number of infused platelets were performed. Posttransfusion platelet increments were related to the HLA matching of donor-recipient pairs and to leukocyte crossmatch tests in vitro. The transfusion response displayed a striking difference depending on the absence (type-O match) or presence ( type1 or -2 match) of donor HLA antigens differing from the recipient. Whereas 95% of transfusions from type-O match donors resulted in a compatible platelet increment, only 20% successful transfusion responses could be achieved with typo-i or -2 match donors. In 77% of typo-i or -2 match transfusions with poor posttransfusion platelet increments, the lymphocyte cytotoxicity test ( incubation time 1 80 mm at room temperature) was positive. This test therefore seems to be a useful tool in predicting the outcome of transfusion responses in typo-i and -2 match pairs. In contrast, the lymphocyte cytotoxicity tests were of no predictive value in typo-O match pairs. The influence of specific antigranulocyte antibodies on type-O match platelet transfusions was assessed in four recipients. Although severe transfusion reactions were observed, no detrimental influence on platelet increments could be observed, at least following the initial transfusion.