Platelet aggregating activity of plasma in patients with thrombotic thrombocytopenic purpura evaluated by a particle counting method using light scattering

The platelet aggregating activity of plasma obtained from five patients wit h thrombotic thrombocytopenic purpura (TTP) was evaluated by a particle cou nting method using light scattering. When normal platelets were suspended i n the plasma obtained from TTP patients, small aggregate formation was obse rved after stirring at 1000 rpm without the addition of platelet aggregatin g agents; no aggregate was observed, however, in the plasma obtained from h ealthy donors. Since the inhibitory effect of the addition of normal plasma to TTP plasma on this reaction was dose-dependent and not additive, the ef ficacy 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 T TP, dipyridamole was more effective for the inhibition of this reaction tha n aspirin. This spontaneous platelet aggregation reaction by a particle cou nting method using light scattering could be useful for evaluating the plat elet aggregating activity in patients with TTP. (C) 1999 The Japanese Socie ty of Hematology.