Post-transfusion purpura: an enigma of alloimmunization.

A patient with post-transfusion purpura is reported. This female patient, sensitized by previous blood transfusion, developed symptomatic thrombocytopenia seven days after a second blood transfusion. A platelet antibody, which had anti-P1A1 specificity, was identified by 51Cr-release assay and by indirect immunofluorescence. Hemorrhage stopped abruptly after plasma exchange therapy. Thrombocytopenia did not recur when the patient was further challenged with P1A1-positive blood and plasma. Anti-P1A1 antibody, detectable by immunofluorescence but not by complement-dependent platelet cytoxicity, persisted in high titer for at least one year after recovery. The heterogeneity and pathogenesis of this clinical syndrome are discussed.