Procoagulant activity of platelets.

A simplified, semiautomated, quantitative method to evaluate platelet procoagulant activity was evaluated on plasma that contained widely divergent concentrations of platelets. When fewer than 100,000 platelets/cu mm were present, excellent correlation between platelet concentration and clotting time was noted, with correlation best in the range 30,000 to 100,000 platelets/cu mm. When platelets were present in concentrations greater than 100,000/cu mm, no alteration in clotting time as a function of platelet count was noted. These observations were consistent with clinical observations that patients with greater than 100,000 platelets rarely bleed and that those with fewer than 30,000 platelets bleed in an unpredictable fashion. The procedure appears to be of potential value in evaluation of patients for defects in platelet factor 3 release.