In vitro test of phagocytic ability of human platelets using colloidal carbon

A simple and reproducible test for phagocytic ability of human platelets are described. Platelets obtained from heparinized venous blood were incubated with colloidal carbon (particle diameter = 0.11 micron) in autologous plasma at 37 degrees C. The number of platelets with or without carbon particles on smear preparations was determined at fixed intervals. Electron microscopic observation confirmed the apparent inclusion of carbon particles in platelets as being an internalization of these particles in the vesicular or canalicular structures. Under optimum conditions, the percentage of phagocytosis-positive platelets in healthy donors was 66.6 +/- 14.3 (S.D.)% and the reproducibility of the test was considered to be satisfactory. There was no significant difference between men and women.