Kinetics of 111In-labelled platelets in healthy subjects

25 healthy subjects underwent platelet kinetic and scintigraphic studies following injection of 111In-labelled platelets. Using the multiple hit model, platelet mean lifetime averaged 185.3 hours (range 141.2-225.6), and platelet in vivo recovery averaged 56% (range 42-89). The platelet disappearance pattern was almost linear. However, in comparison with simultaneously injected 51Cr-labelled platelets (7 subjects studied), the 111In-platelet survival curves were slightly more curved. Our results indicate that this may be ascribed to a slight degree of elution of 111In from the circulating platelets. The plateau or even slight increase in circulating activity following the initial steep decline in activity appears mainly to reflect reversible sequestration of platelets in the spleen and maybe in the liver. Using a semiquantitative scintigraphic approach, we estimated 45%, 25% and 30% platelet destruction to occur in the spleen, liver and bone marrow, respectively. Our results indicate that the discrepancy between the course of circulating platelet-bound activity and of chest wall activity reflects platelet destruction in the bone marrow.