A flow cytometric platelet immunofluorescence crossmatch for predicting successful HLA matched platelet transfusions.

Platelet crossmatching may provide a useful way of selecting donors for effective platelet transfusions in patients refractory to random donor platelet concentrates due to alloimmunization. We assessed the predictive value of a flow cytometric platelet immunofluorescence crossmatch test for the outcome of HLA matched platelet transfusions in a group of alloimmunized patients. Platelet immunofluorescence (PIFT) crossmatches were performed for 104 HLA-matched platelet transfusions administered to 30 patients. A negative PIFT crossmatch correctly predicted a successful platelet transfusion (1 h post-transfusion platelet recovery >20%) in 56/75 (75%) cases. We also considered non-immunological factors that, in combination with alloimmunization, might have contributed to an unsuccessful transfusion result, i.e. fever, septicaemia, splenomegaly, disseminated intravascular coagulation and bleeding. The predictive value of a negative PIFT crossmatch was better when these non-immunological factors were absent [48/59 (81%) correct predictions] than when these factors were present [8/16 (50%) correct predictions] (P=0.01; chi-square test). The effect of ABO incompatibility between donor and recipient on the predictive value of the PIFT crossmatch was also analysed. Positive PIFT crossmatches occurred more frequently in ABO incompatible donor-recipient combinations [in 18/28 (64%) cases] than in ABO-compatible donor-recipient combinations [in 11/76 cases (14%)] (P<0.001, chi-square test). Successful platelet transfusions were observed on 53/76 (70%) occasions in ABO compatible transfusions as compared to 16/28 (57%) in ABO incompatible transfusions. This difference was not statistically significant (P=0.23; chi-square test). Consequently, a negative PIFT crossmatch appeared to be non-predictive for the transfusion outcome in cases of ABO incompatibility between donor and recipient. We conclude that the PIFT crossmatch for platelet donor selection in addition to matching for HLA antigens, is predictive for the outcome of ABO compatible transfusions in alloimmunized recipients and prediction levels are increased when non-immunological causes for platelet refractoriness are absent.