Background: The seasonal epidemic of Kawasaki disease (KD) in winter in Japan suggests that low vitamin D status may affect KD through the immune system. We aimed to evaluate the effect of vitamin D on the onset and clinical course of KD. Methods: We conducted a case-control study to compare 25-hydroxyvitamin D (25(OH)D) levels in KD patients admitted to our hospital between March 2018 and June 2021, with those in healthy controls from published Japanese data. In patients with KD, we evaluated the association of 25(OH)D levels with intravenous immunoglobulin resistance and coronary artery lesions. Results: We compared 290 controls and 86 age-group-adjusted patients with KD. The 25(OH)D levels in KD patients were lower than those in the controls (median: 17 vs. 29 ng/mL, P < 0.001). In winter, 25(OH)D levels in KD patients were lower than those in summer (median: 13 vs. 19 ng/mL). The adjusted odds ratios for the onset of KD were 4.9 (95% CI: 2.5-9.6) for vitamin D insufficiency (25(OH)D: 12-20 ng/mL) and 29.4 (95% CI: 12.5-78.2) for vitamin D deficiency (25(OH)D < 12 ng/mL). Among 110 KD patients, 25(OH)D levels at diagnosis of KD were not associated with intravenous immunoglobulin resistance or coronary artery lesions. Conclusions: The 25(OH)D levels in patients with KD were lower than those in the controls, especially in winter. Lower 25(OH)D levels in winter were associated with an increased risk of KD onset. It remains to be elucidated whether the observed association has a causal relationship.Key words 25-hydroxyvitamin D, coronary aneurysm, intravenous immunoglobulin, Kawasaki disease, vitamin D deficiency.Kawasaki disease (KD) is an acute systemic vasculitis of unknown cause that primarily affects infants and children. 1 Seasonal and regional epidemics have been reported and, in Japan, KD is most prevalent in winter, with a small peak in summer. 2 These epidemics have suggested that some infections trigger KD. 2 Vitamin D is an essential nutrient that is synthesized in the skin upon exposure to ultraviolet rays, in addition to absorption from food. 3 Vitamin D was initially reported to play an important role in bone metabolism and calcium homeostasis but recently, it has been recognized that it regulates innate and adaptive immunity. 3,4 Vitamin D status was defined based on serum 25-hydroxyvitamin D (25(OH)D) levels because of its relatively long half-life. 4 We hypothesized that lower 25(OH)D levels, especially in winter, predispose host immunity to exacerbate the onset and progression of KD. To test this hypothesis, we first conducted a case-control study comparing KD patients and previously reported healthy controls. Second, in patients with KD, we evaluated whether 25(OH)D levels at diagnosis were associated with the clinical course of KD, such as intravenous immunoglobulin (IVIG) resistance or coronary artery lesions (CALs). We have also considered the effect of breastfeeding as a possible confounding factor, which has been reported to be associated with a lower risk of KD and often leads to reduced ...

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Background: After changing the urinary protein assay method from the pyrogallol red (PR) method to the benzethonium chloride (BC) method in 2019, the number of patients with a urinary protein-to-creatinine ratio (PCR) of 0.15 g/gCr or more increased. This study aimed to investigate the possible causes behind this increase. Methods: The subjects were elementary and junior high school students who had undergone urinalysis in our hospital at least once a year for 3 consecutive years from April 2017 and whose diagnoses were no abnormality or asymptomatic hematuria. The urinary PCR of the earliest morning samples were analyzed. Results: The participants were 74 patients (22 men and 52 women) with a median age of 12.3 years in 2019. The median urinary PCR was higher in 2019 using the BC method (0.14 g/gCr) than in 2017 and 2018 using the PR method (0.09 and 0.08 g/gCr, respectively). Conclusion: When the BC method was used to assess urinary protein, the PCR tended to be higher than that in the PR method. When evaluating the PCR, the urinary protein assay used should be noted.