Prolonged thrombocytopenia in post‐transfusion purpura (PTP) associated with changes in the crossed immunoelectrophoretic pattern of von Willebrand factor (vWF), circulating immune complexes and endothelial cell cytotoxicity

S ummary . A 39‐year‐old multigravida presented with a platelet count of 2 × 10 9 /l 12 d after a blood transfusion. The clinical presentation was typical of post‐transfusional purpura (PTP). She was successfully managed with intensive plasma exchange with plasma replacement. Replacement with albumin saline was unsuccessful. Elevated levels of immune complexes were detected on presentation but were reduced to normal levels by plasma exchange but were elevated again during relapse. Raised levels of circulating platelet aggregates and platelet‐aggregating activity were found during relapse but were absent during remission. Crossed immunoelectrophoresis of vWF showed a left shift suggesting the presence of abnormally high molecular weight multimeric forms. In contrast, multimeric assay of the same samples were within normal limits suggesting that the shift noted on crossed immunoelectrophoresis may have resulted from complexing of vWF with some other components. Immunological studies demonstrated the presence of endothelial cell cytotoxicity and lymphocytotoxicity in the patient's serum. It is concluded that the thrombocytopenia observed in PTP may not occur as a direct result of the immunological event initiating the disorder but rather indirectly via the release of vWF consequent upon endothelial cell damage which, either alone or in combination with another factor, possibly immune complexes, induces intravascular platelet aggregation and sequestration. There were significant