Post‐transfusion purpura associated with alloimmunization against the platelet‐specific antigen, baka

Abstract

Post-transfusion purpura (PTP) with severe thrombocytopenia occurred eight days after transfusion in a 28-year-old woman and responded to treatment with prednisone and plasma exchange. In contrast to nearly all previously studied cases of PTP, the patient's platelets were PI^AI-positive and anti-PI^AI antibody could not be detected in serum obtained during the thrombocytopenic episode. Her serum was found to contain an antibody specific for a recently described platelet-specific alloantigen, Bak^a, in addition to multiple HLA-specific antibodies. The patient's platelets, typed following recovery, were Bak^a-negative. These findings indicate that post-transfusion purpura can occur in association with alloimmunization to platelet-specific antigens other than PI^AI. In performing the serologic studies, a close relationship and possible identity between Bak^a and another recently reported platelet antigen, Lek^a, was observed. A method for analyzing mixtures of cytotoxic platelet-reactive antibodies without separating the individual antibodies is described.