Retrospective evaluation of flow cytometry as a platelet crossmatching procedure

We performed a retrospective analysis of flow cytometry as a platelet crossmatching procedure. Sera from 17 alloimmunized refractory patients were tested against 32 donor platelets, which had been stored as platelet-rich plasma for up to 36 months. Overall, 14/32 (44%) crossmatches were positive. The mean 1 h posttransfusion corrected count increments (CCIs) were 9,195 and 2,269 for a negative and a positive crossmatch, respectively. The predictive value of a positive crossmatch was 86%, whereas the predictive value of a negative crossmatch was 56%. When samples with low background fluorescence or with high panel-reactive antibody (PRA) levels were evaluated separately, the accuracy of the crossmatch improved from 69% to 80%. When compared to the platelet adhesion immunofluorescence test (PAIFT) and the standard and antiglobulin-enhanced lymphocytotoxicity tests for the detection of HLA antibodies, flow cytometry appeared to be more sensitive. We conclude that flow cytometry is a useful technique for platelet crossmatching, particularly for alloimmunized patients for whom HLA compatible platelets may not be readily available.