Clinical implications of thrombocytosis in acute phase Kawasaki disease

In Kawasaki disease (KD), thrombocytosis is commonly found in the subacute phase. However, the exact significance of thrombocytosis in the acute phase of KD is unclear. To evaluate serum platelet counts in patients during the acute phase of KD and assess the clinical outcomes according to the degree of thrombocytosis, we collected data of KD patients between 2009 and 2017. A total of 505 patients with KD were enrolled, and 249 (49.3%) patients had thrombocytosis, including mild (69.5%), moderate (21.7%), severe (4.8%), and extreme (4.0%) thrombocytosis. Correlation analysis revealed a positive correlation between the maximum platelet count and admission duration (r = 0.359, p < 0.001) and fever duration (r = 0.204, p < 0.001). The maximum platelet count was significantly higher in IVIG non-responders than that in IVIG responders (629 ± 201 × 10⁹/L vs. 499 ± 154 × 10⁹/L, p < 0.001), and in patients with coronary artery dilatation (CAD) than in those without CAD (602 ± 201 × 10⁹/L vs. 512 ± 164 × 10⁹/L, p < 0.001).Conclusion: Thrombocytosis in acute phase KD was associated with poor clinical outcomes such as IVIG non-responsiveness, CAD, and prolonged admission and fever durations. What is Known: • Thrombocytopenia in the acute phase of KD is related to non-responsiveness to IVIG and the risk of coronary artery dilatation. • The exact significance of thrombocytosis in the acute phase of KD as a benign phenomenon or a signal of poor outcome of KD is unclear. What is New: • Thrombocytosis in acute phase KD was associated with poor clinical outcomes such as IVIG non-responsiveness, CAD, and prolonged admission and fever durations.