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Platelet aggregation velocity was measured with an aggregometer in platelet-rich plasma from 34 normal subjects following addition of ADP, collagen, or epinephrine. Platelet volume parameters mean, mode, megathrombocyte index (large platelets) were determined with a model B Coulter Counter attached to a P64 Channel Analyzer with electronic recorder and correlated with platelet count. A negative linear relationship was found between platelet count and platelet volume (r = –0.53, p 0.1, respectively). Platelet volume distribution curves of residual nonaggregated platelets revealed a relative absence of larger platelets. Thus, platelet aggregation velocity was proportional to platelet volume, but correlated best with the number of large platelets or megathrombocyte index, particularly with ADP-induced platelet aggregation. It is suggested that the clinical strategy for treatment of platelet disorders would be better directed toward evaluation of platelet size and function rather than number, and that experimental as well as therapeutic procedures for the harvesting of platelets be directed toward a method of collection in which a portion of the megathrombocyte population is not routinely discarded.
Simon Karpatkin (Wed,) studied this question.