A cross-sectional retrospective study to analyze the underlying causes and clinical characteristics of children with reactive thrombocytosis at a Korean tertiary medical center

BACKGROUND: Reactive thrombocytosis (RT) is a common condition among children, although no studies have examined the etiology or clinical characteristics of RT among Korean children. METHODS: This retrospective study evaluated children with RT at a single Korean tertiary center during a 10-year period. RESULTS: RT accounted for 13.5% of children who were admitted to the pediatric ward (4,113/30,355): mild RT, 82.7%; moderate RT, 14.1%; severe RT, 1.1%; and extreme RT, 2.1%. There was a negative correlation between platelet count and Hb level (P=0.008). There were positive correlations between platelet count and WBC (P=0.001), erythrocyte sedimentation rate (ESR) (P=0.007), and admission duration (P=0.006). The most common cause of RT was infection and the second most common was Kawasaki disease (KD). The highest proportion of lower respiratory tract infection was observed in extreme RT (P<0.001). The proportion of KD was highest in extreme RT (P<0.001) and in children aged 1–7.9 years (P<0.001). The proportion of refractory KD was highest in extreme RT (P=0.005). In cases of KD, there was a positive correlation between platelet count and fever duration (P=0.006). Non-KD autoimmune inflammation was only observed in mild/moderate RT, and its proportion was highest in children aged 8–18 years (P<0.001). CONCLUSION: In children, more severe RT was associated with lower Hb, increased WBC, ESR, and prolonged admission. With respiratory infection or KD, extreme RT was associated with more severe disease course.