Supplementary Material for: Association between Hypouricemia and Reduced Kidney Function: A Cross-Sectional Population-Based Study in Japan

<b><i>Background:</i></b> Hypouricemia, conventionally defined as a serum uric acid level of ≤2 mg/dl, is considered a biochemical disorder with no clinical significance. However, individuals with renal hypouricemia have a high risk of urolithiasis and exercise-induced acute kidney injury, both of which are risk factors for reduced kidney function. <b><i>Methods:</i></b> To test the hypothesis that individuals with hypouricemia would be at a higher risk of reduced kidney function, we conducted a population-based cross-sectional study using data from the Specific Health Checkups and Guidance System in Japan. Logistic analysis was used to examine the relationship between hypouricemia and reduced kidney function, defined as estimated glomerular filtration rate &lt;60 ml/min/1.73 m². <b><i>Results:</i></b> Among 90,710 men (mean age, 63.8 years) and 136,935 women (63.7 years), 193 (0.2%) and 540 (0.4%) were identified as having hypouricemia, respectively. The prevalence of hypouricemia decreased with age in women (p for trend &lt;0.001), but not in men (p for trend = 0.24). Hypouricemia was associated with reduced kidney function in men (odds ratio, 1.83; 95% confidence interval, 1.23-2.74), but not in women (0.61; 0.43-0.86), relative to the reference category (i.e., serum uric acid levels of 4.1-5.0 mg/dl) after adjusting for age, drinking, smoking, diabetes, hypertension, hypercholesterolemia, obesity, and history of renal failure. Sensitivity analyses stratified by diabetic status yielded similar results. <b><i>Conclusions:</i></b> This study is the first to provide evidence that hypouricemia is associated with reduced kidney function in men. Further research will be needed to determine the long-term prognosis of individuals with hypouricemia.