Thrombocytosis in low birthweight infants: a physiological phenomenon in infancy.

Prematurity has traditionally been connected with thrombocytopenia, although this is unlikely to be associated with prematurity itself but rather with serious illnesses in such infants. Platelet counts were measured in 117 healthy preterm infants with birthweights less than 2000 g, who were followed up from 2 weeks to 6 months. In this series the platelet counts were high compared with those in previous reports, and also compared with what is considered normal for term infants. The 95% range was between 160 and 675 X 10(9)/1, with a median value of 375 X 10(9)/1. The data suggest that thrombocytosis is a phenomenon related to prematurity.