Thrombocytosis in pediatric patients is associated with severe lower respiratory tract inflammation.

Background: Secondary thrombocytosis is associated with a variety of clinical conditions. The aim of this study was to determine the incidence and to analyze the clinical significance and prognostic value of thrombocytosis in lower respiratory tract infection.

Methods: A total of 102 pediatric patients were hospitalized with lower respiratory tract infection during a period of 30 months.

Results: Forty nine (48%) of those patients had platelet counts >500 x 10(9)/L. The median age of the thrombocytotic patients was 31 months as opposed to 61 months for the non-thrombocytotic ones. The patients with thrombocytosis had more serious illness. This is indicated by three factors: more severe clinical condition on admission, presence of respiratory distress and longer hospitalization. Sedimentation rate >70 mm/h was observed in 44.4% patients of the thrombocytotic group compared to only 27.7% of the non-thrombocytotic ones. Almost all patients with pleural effusion were thrombocytotic. The children with very high platelet counts >650 x 10(9)/L presented with respiratory distress on admission and required longer hospitalization time. No other significant clinical or laboratory differences were demonstrated between these patients and the remainder of the thrombocytotic patients.

Conclusions: Thrombocytosis is a common finding among patients with lower respiratory tract infection. Thrombocytotic patients have a more severe clinical condition. Importantly, thrombocytosis occurs almost exclusively in patients with pleural effusion. The platelet count may be a useful clinical marker associated with the severity of the lower respiratory tract infection.