INCREASED PLATELET RETENTION IN FAMILIAL RECURRENT THROMBOTIC THROMBOCYTOPENIC PURPURA

We studied two brothers with recurrent thrombotic thrombocytopenic pur pura (TTP). Platelet retention, measured with a modified Adeplat S gla ss-bead test, was found to be increased during acute episodes of TTP a nd during remissions. Values of platelet retention ranged between 57 t o 95% (normal range 16 to 34%). The continually elevated values enable d us to investigate which fraction of the patients' blood was responsi ble for the increased platelet retention and to evaluate the effect of different treatments on this parameter. We found that the patients' p lasma increased the retention of normal platelets and of platelets tak en from a patient with von Willebrand's disease type III. This activit y was located in the cryoprecipitate fraction of plasma. Unusually lar ge von Willebrand factor (VWF) multimers were demonstrated in both chi ldren during remission and decreased during relapse. Both fresh frozen plasma (FFP) and a commercial factor VIII/vWF concentrate reduced pla telet retention when tested during remission. Treatment of both siblin gs with FFP or factor VIII/vWF concentrate was beneficial during recur rences. We conclude that the elevated platelet retention is due to a f actor in the cryoprecipitate of the childrens' plasma, and that both F FP and factor VIII/vWF concentrate are effective in decreasing platele t retention.