Thrombocytosis and infections in childhood.

In both children and adults, thrombocytosis is usually defined as a platelet count of more than 450 10/ L. As there are many primary and secondary causes, as well as false or “spurious” conditions mimicking thrombocytosis, establishing the cause requires considering clinical features and hematologic parameters. Pediatric primary thrombocytosis is very rare, but reactive thrombocytosis (RT) can be frequently observed in children with infections, iron deficiency, tissue damage, hemolysis, autoimmune diseases, malignancies, and other causes of an acute-phase response. The incidence of secondary forms due to infections is significantly higher in childhood than in adulthood, and infections are the main cause of pediatric RT, with reported incidence rates ranging from 37% to 78%. This wide range may be explained by the cutoff platelet count, the study population (in-patients, outpatients, or both), and the median age of the enrolled subjects.