Effect of injected heparin on platelet levels in man.

Platelets from six normal subjects were labelled with radiochromate and reinfused into their donors. Subsequently, the effect of intravenously injected heparin upon the levels of circulating platelets and platelet radioactivity was studied. Although reductions in platelet counts occurred in three subjects following single injections of 10,000 units, these changes were not reflected in the levels of circulating platelet radioactivity. It is concluded that the alterations in platelet counts observed were probably due to an effect of heparin in vitro. The experimental evidence that heparin induces thrombocytopenia in vivo, in man, is unconvincing.