Etiology and clinical course of severe and extreme thrombocytosis in children: a retrospective single-center study

The aim of this study was to describe the etiology and clinical course in children with severe thrombocytosis (ST, platelet counts > 900 x 10(9)/L) and extreme thrombocytosis (ET, platelet counts > 1000 x 10(9)/L) in a tertiary pediatric hospital. Patients aged 0-18 years with platelet counts over 900 x 10(9)/L who were admitted to our hospital were analyzed. Thrombocytosis was defined as a platelet count exceeding 450 x 10(9)/L. Thrombosis was diagnosed based on computed tomography scans or ultrasound findings. Potential factors associated with the development of extreme thrombocytosis were identified using logistic regression models. Only one (0.8%) out of the 120 patients identified with ST (n = 61) and ET (n = 59) had primary thrombocytosis. The most common underlying condition was congenital heart disease (26.7%), followed by Kawasaki disease (16.7%). With the exception of the hemoglobin level, no major differences were found for the baseline characteristics between the ST and ET groups. A lower hemoglobin level (< 10.0 g/dL) at the onset of thrombocytosis was identified as a predictor for ET development (adjusted odds ratio 2.73, 95% confidence interval 1.18-6.28). Overall, 56 of 120 (46.7%) patients received aspirin therapy. Venous thrombosis occurred in one (0.8%) patient. Conclusions: We found a low proportion of primary thrombocytosis and a low incidence of thrombosis in children with ST and ET. Our results suggest that pediatric ST and ET may share common characteristics and may have features that are distinct from those in adults. What is Known: center dot Secondary thrombocytosis is a frequent finding in children. center dot Adult extreme thrombocytosis has been found to be associated with primary thrombocytosis. What is New: center dot There were no major differences in the baseline characteristics between children with severe and extreme thrombocytosis. center dot The incidence of thrombosis was markedly low in both severe and extreme thrombocytosis groups.