Platelet-reactive HLA antibodies associated with low posttransfusion platelet increments:: a comparison between the monoclonal antibody-specific immobilization of platelet antigens assay and the lymphocytotoxicity test

BACKGROUND: Platelet-reactive HLA antibodies are a major reason for low posttransfusion platelet increments. The clinical importance and value of the test systems for their in vitro determination is still controversial. STUDY DESIGN AND METHODS: A prospective analysis of HLA antibodies was performed in sera obtained once a week for at least 4 consecutive weeks from 55 patients (female/male, 28/27; age: median, 49 years; range, 18-69) undergoing intensive chemotherapy and in need of prophylactic platelet transfusions. All sera (n = 330) were analyzed by the monoclonal antibody-specific immobilization of platelet antigens (MAIPA) assay and by the standard lymphocytotoxicity test (LCT). RESULTS: In the MAIPA, 24.5 percent of sera (81/330) obtained from 22 patients contained HLA antibodies. These were detected significantly more often by the MAIPA assay than by the LCT (24.5% vs. 8.2%). Fifty-five sera (20 patients) were positive in the MAIPA assay only. In 15 patients, HLA antibodies were transient. In 3 patients, HLA antibodies were detected earlier by the MAIPA assay than by the LCT. Significantly more sera obtained at the time of low posttransfusion platelet increments were positive in MAIPA alone, rather than in both MAIPA and the LCT (44% vs. 17%). CONCLUSION: The MAIPA assay is more sensitive than the standard LCT in detecting platelet-reactive HLA antibodies. These MAIPA-positive/LCT-negative HLA antibodies affect the posttransfusion platelet increment.