Association between blood urea nitrogen-to-albumin ratio and kidney stones: A cross-sectional study based on NHANES

Kidney stones are a disorder in which urinary solutes precipitate to form crystalline aggregates in the urinary space. The blood urea nitrogen-to-albumin ratio (BAR), a common inflammatory indicator, has an unclear association with kidney stones. Using NHANES 2007–2020 data, we compared baseline characteristics between kidney stone formers and controls and evaluated the BAR–stone relationship via weighted multivariate logistic regression (WMLR), restricted cubic splines (RCS), stratification analyses, and XGBoost, with validation in an independent external cohort. Twenty baseline features, including BAR and age, differed significantly between groups (P < 0.05). In all WMLR models, BAR was positively and nonlinearly associated with kidney stone risk (OR > 1, P < 0.05). Subgroup analyses revealed stable associations in females (OR = 1.10, P < 0.001), low vitamin A intake (OR = 1.10, P < 0.001), high water intake (OR = 1.11, P < 0.001), age < 50 years (OR = 1.14, P < 0.01), and education less than high school (OR = 1.11, P < 0.01). XGBoost identified BAR and water intake as prominent risk factors (AUC = 0.658). External validation confirmed a positive association (Model 1 OR = 1.029, 95% CI 1.016–1.043; Model 2 OR = 1.030, 95% CI 1.016–1.044; Model 3 OR = 1.029, 95% CI 1.015–1.045; all P < 0.001), and RCS confirmed a nonlinear dose–response relationship (nonlinear P = 0.0006). Subgroups aged ≥ 60 years, males, and females showed significant associations (ORs = 1.027–1.034). In XGBoost, BAR was the most important predictor (Gain = 0.265). These findings reveal a significant association between BAR and kidney stones, offering theoretical insights for prevention and risk stratification; BAR may serve as a valuable marker in kidney stone management.