Leukocyte counts in patients with Kawasaki disease: from the results of nationwide surveys of Kawasaki disease in Japan

In the latest survey of Kawasaki disease in Japan, questionnaires on maximal leukocyte counts of the patients were included to clarify whether leukocyte counts could be of value for the diagnosis and prediction of outcome. A questionnaire form and diagnostic guidelines for Kawasaki disease were sent to all pediatric departments of hospitals with ≥100 beds throughout Japan, and information including maximal leukocyte counts was obtained on patients with Kawasaki disease diagnosed during the 2-y period from January 1993 to December 1994. Of the 11 458 patients diagnosed during the 2-y period, maximal leukocyte counts were reported in 11 062 patients (96.5%). The mean value and the distribution of maximal leukocyte counts were lower in the age group under 1 y. The mean values and the distribution of leukocyte counts were lowest in suspected cases among three diagnostic categories: typical cases of Kawasaki disease, atypical cases, and suspected cases. The mean values of maximal leukocyte counts of the patients with cardiac sequelae were significantly higher than those without cardiac sequelae in each age group. The proportion of patients with cardiac sequelae increased with leukocyte counts in each age group. The Receiver/Response Operating Characteristic (ROC) curve for maximal leukocyte counts in Kawasaki disease revealed that the accuracy of maximal leukocyte counts for prediction of cardiac sequelae was highest in the age group <6 months, and the most accurate cut-off point was 16 × 10⁹/l. The strongest association between higher leukocyte counts (≥16 × 10⁹/l) and cardiac sequelae was observed in the age group <6M. A large-scale analysis of leukocyte counts in patients with Kawasaki disease revealed age-dependent relationship between maximal leukocyte counts, diagnostic categories and outcome. Maximal leukocyte counts may be helpful for the prediction of outcome with the consideration of age.