Thrombocytosis in childhood: a survey of 94 patients.

The introduction of the newer generation of electronic cell counters allows the routine reporting of platelet numbers when the peripheral blood count is requested. In a 12-month period, 100 episodes of marked thrombocytosis (platelet count more than 900 X 10(9)/L) were found among 94 children. These patients were young (median age 9 months). All but one episode of marked thrombocytosis occurred as a phenomenon secondary to a variety of disease states. Infections, especially those involving the central nervous systems were the commonest cause of an elevated platelet count in this series. Malignant diseases alone were rarely associated with thrombocytosis of this magnitude. The elevated platelet count began to decline at a mean of 3 days after diagnosis, and no thrombotic or hemorrhagic complications were encountered. Marked thrombocytosis is a benign, common phenomenon in young children, but specific treatment is not required.