Unusually Large Plasma Factor VIII: von Willebrand Factor Multimers in Chronic Relapsing Thrombotic Thrombocytopenic Purpura

A platelet-agglutinating factor has been detected in the plasma of some patients during episodes of thrombotic thrombocytopenic purpura (TTP).1 , 2 Agglutination induced in vitro by this plasma factor is inhibited by normal plasma and does not require platelet production of the arachidonic acid metabolite thromboxane A2, release of granule contents, platelet metabolism, or calcium or magnesium ions.3 These characteristics are similar to those of agglutination induced in vitro by the attachment to platelets of large, multimeric, von Willebrand factor components of the factor VIII complex (VIII:vWF), and this similarity led us in the present study to investigate the properties . . .