Red blood cell distribution width to albumin ratio as a predictor of gallstones in US adults: a NHANES-based cross-sectional study

The red blood cell distribution width-to-albumin ratio (RAR) is an indicator of the body’s inflammatory condition and is associated with several diseases. RAR may be clinically relevant given that inflammation is involved in gallstone formation. However, its association with the development of gallstones remains unclear. This study aimed to explore the relationship between RAR and gallstones. This population-based cross-sectional study analyzed data from 5800 American adults aged ≥ 20 years, in the National Health and Nutrition Examination Survey (NHANES) 2017–2020. Three multivariate logistic regression models (adjusted for demographics, behaviors, and comorbidities) and a restricted cubic spline (RCS) model were constructed to evaluate the association between RAR and gallstones. Sensitivity analyses, which included stratification and interaction analyses, were performed to identify the population of interest and evaluate the possible interactions between RAR and gallstones. The study included 5,800 participants with complete data, of whom 620 (10.7%) had gallstones. RCS analysis indicated a positive correlation between RAR levels and the presence of gallstones. Fully adjusted multivariate logistic regression revealed that each 1-unit increase in RAR was significantly associated with elevated gallstone risk (OR = 1.25, 95% CI: 1.06–1.47; P = 0.008). Compared to the low RAR group, the high RAR group showed a significantly increased gallstone risk (OR = 1.40, 95% CI: 1.09–1.81; P = 0.010). Subgroup analyses indicated that the populations of special concern included individuals aged ≥ 50 years, females, widowed/divorced/separated, smokers, non-diabetic, non-hypertensive, and non-coronary heart disease individuals. This is the first study to explore the direct positive relationship between RAR and the likelihood of developing gallstones. Its low cost and routine accessibility makes RAR a practical tool for early risk stratification, particularly in high-prevalence populations. Further longitudinal studies are required to confirm causality and clinical applicability.