Thrombopoietin and Interleukin-6 in Children with Pneumonia-Associated Thrombocytosis

The aim of this study was to investigate why some, but not all, children develop thrombocytosis during the course of pneumonia. The retrospective study included 40 healthy children and 75 children with pneumonia: 17 patients with platelet count within the reference values, i.e., platelet count ≤450 × 10 9/L, and 58 with thrombocytosis >450 × 10 9/L. Erythrocyte sedimentation rate, leukocyte and platelet counts, and concentrations of hemoglobin, C-reactive protein, interleukin-6 and thrombopoietin were determined in the blood of patients and control groups of children. Patients with thrombocytosis were slightly younger (3.0 ± 1.8 years and median 2.5 years, respectively) than patients with normal platelet count (3.8 ± 2.4 years and median 4 years, respectively). Additionally, according to clinical and radiological findings, pneumonia in children with thrombocytosis had a more severe and protracted course. Serum thrombopoietin concentrations were found to be 91.2 ± 41.7 ng/L (range: 14.3–166.7 ng/L) in patients with normal platelet count (313 ± 70 × 10 9/L, range: 206–428 × 10 9/L). In patients with thrombocytosis (581 ± 131 × 10 9/L, range: 450–830 × 10 9/L) serum thrombopoietin ranged from 63.6 to 1115.9 ng/L (526.6 ± 268.4 ng/L). In these patients both concentration of hemoglobin (114 ± 12 g/L) and iron (4.3 ± 1.3 μmol/L) significantly decreased as compared with the control group. Study results suggested the possible development of reactive thrombocytosis in children with pneumonia. As platelets are involved in inflammatory reaction, reactive thrombocytosis might be part of the mechanism of defense. Reactive thrombocytosis may develop as a sequel of either anemia or inflammatory reaction (or both).