Platelet aggregating activity of plasma in patients with thrombotic thrombocytopenic purpura evaluated by a particle...

The platelet aggregating activity of plasma obtained from five patients with thrombotic thrombocytopenic purpura (TTP) was evaluated by a particle counting method using light scattering. When normal platelets were suspended in the plasma obtained from TTP patients, small aggregate formation was observed after stirring at 1000 rpm without the addition of platelet aggregating agents; no aggregate was observed, however, in the plasma obtained from healthy donors. Since the inhibitory effect of the addition of normal plasma to TTP plasma on this reaction was dose-dependent and not additive, the efficacy of plasma therapy was not confirmed. Small aggregates were formed in the high molecular weight fraction (HMWF) of TTP plasma but not in the low molecular weight fraction (LMWF), suggesting that the platelet aggregating activity existed in HMWF. Among the antiplatelet agents usually used for TTP, dipyridamole was more effective for the inhibition of this reaction than aspirin. This spontaneous platelet aggregation reaction by a particle counting method using light scattering could be useful for evaluating the platelet aggregating activity in patients with TTP.