Association between serum uric acid to HDL-C ratio and ultrasound-defined fatty liver and the statistical decomposition involving BMI and fasting blood sugar: a secondary analysis of Japanese adults

The serum uric acid-to-HDL-C ratio (UHR%) has been proposed as a composite biomarker of metabolic imbalance. However, its dose–response association with ultrasound-defined fatty liver and the extent to which obesity-related factors statistically account for this association remain unclear. We aimed to evaluate the association between UHR% and prevalent ultrasound-defined fatty liver in Japanese adults, assess its discriminatory performance, and quantify the proportion of the association statistically explained by body mass index (BMI) and fasting blood sugar (FBS). This cross-sectional secondary analysis included 911 Japanese adults undergoing routine health checkups between 2004 and 2012. Multivariable logistic regression was used to evaluate the association between UHR% and ultrasound-defined fatty liver after adjustment for demographic, lifestyle, and metabolic covariates. Spline-based analysis was used to examine the dose–response pattern. Receiver operating characteristic (ROC) analysis compared the discrimination of UHR% with standalone serum uric acid, standalone HDL-C, and a two-variable model including both components separately. A statistical decomposition analysis estimated the proportion of the observed association statistically explained by BMI and FBS. In the fully adjusted model, each 1-standard deviation increase in UHR% was associated with higher odds of ultrasound-defined fatty liver (OR = 1.97, 95% CI 1.50–2.58; P < 0.001). Spline-based dose–response analysis showed no evidence of nonlinearity (χ 2 = 1.52, df = 3, P = 0.678), supporting an approximately linear positive association. In an exploratory, single-cohort ROC analysis, UHR% showed moderate discrimination (AUC = 0.767), performing better than standalone serum uric acid and standalone HDL-C, but not better than the two-variable model including both predictors separately; no calibration assessment or external validation was performed, so these discrimination findings should be interpreted with caution. Statistical decomposition analysis showed that BMI and FBS statistically explained 41.9% and 8.1% of the observed association, respectively. Higher UHR% was independently and approximately linearly associated with prevalent ultrasound-defined fatty liver in this cross-sectional Japanese population. UHR% is statistically associated with metabolic dysregulation in which BMI plays a substantial explanatory role in this cross-sectional study. Although UHR% provided better discrimination than either individual component alone, its standalone screening utility remains unproven and requires prospective validation.