Abnormal platelet von willebrand factor interaction in patients with TTP

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Abstract
Thrombotic thrombocytopenic purpura (TTP) is associated with abnormal platelet function and disturbances in coagulation; however, a specific causative factor is not defined. Plasma infusion or plasma exchange (PE) are thought to be of benefit in replacing a deficient plasma component or removing some toxic compound. In three patients with TTP, samples taken prior to initiation of PE showed high levels of vWF:Ag in the plasma (208, 264, and 321 U/dl), whereas the VIII:C levels were normal. The vWF:Ag multimer patterns of the plasma demonstrated a decrease in the amount of high molecular weight (HMW) forms. Analysis of the platelets from one patient also showed an increase in the HMW multimers. Platelets from all three patients showed a decreased ability to absorb vWF:Ag, with little or no absorption of the HMW forms. Following extensive PE and resolution of disease, the platelets regained their ability to absorb vWF:Ag in the one patient examined.