Platelet Count Variation and Risk for Coronary Artery Abnormalities in Kawasaki Disease

Background: Platelet count is considered as a biomarker for the development of coronary artery abnormalities (CAAs) among Kawasaki disease (KD) patients. However, previous studies have reported inconsistent results. We addressed the controversial association of platelet count with CAAs using a large-scale dataset. Methods: A retrospective cohort study was conducted using KD survey data from Japan (2015–2016; n = 25,448). Classifying patients by intravenous immunoglobulin (IVIG) responsiveness, we described the trends in platelet count using the lowest and highest values along with the specific illness days. Multivariate logistic regression analysis was performed to evaluate the association between platelet count and CAAs, adjusting for relevant factors. Results: Platelet counts rapidly decreased from admission, reached the lowest count at 6–7 days, and peaked after 10 days. Platelet counts in IVIG non-responders decreased with a lower minimum value than IVIG responders, but subsequently rebounded toward a higher maximum. Compared with patients with normal platelet counts (150–450 × 10 9 /L), patients with abnormally high platelet counts (>450 × 10 9 /L) were more likely to have CAAs at admission (adjusted odds ratio: IVIG responders, 1.50 [95% confidence interval 1.20–1.87] and non-responders, 1.46 [1.01–2.12]). By contrast, IVIG non-responding patients whose counts were below normal (<150 × 10 9 /L) after hospitalization were at higher risk for developing CAAs (2.27 [1.44–3.58]). Conclusions: Platelet count varied widely by illness day and was confounded by IVIG responsiveness, which might have contributed to previous inconsistent findings. KD patients with abnormally high platelet counts at admission or abnormally low counts after hospitalization were at higher risk for CAAs.