The Relationship Between Blood Urea Nitrogen to Albumin Ratio (BAR) and Diabetic Foot Ulcer (DFU) in Diabetic Patients

Objective: To examine the association between the blood urea nitrogen-to-albumin ratio (BAR) and diabetic foot ulcer (DFU) among individuals with diabetes, and to determine whether BAR may provide additional value for DFU risk assessment. Methods: Data were obtained from diabetic participants in the National Health and Nutrition Examination Survey (NHANES) 1999–2004. A total of 1337 eligible individuals were included in the final analysis. BAR was calculated by dividing serum urea nitrogen concentration (mg/dL) by serum albumin concentration (g/dL). DFU status was identified according to self-reported questionnaire information. Logistic regression models with progressive adjustment were used to evaluate the association between BAR and DFU. Restricted cubic spline analysis was performed to explore the dose–response pattern, and stratified analyses were conducted to assess whether the association varied across different clinical and demographic subgroups. Results: After full adjustment for potential confounders, higher BAR was significantly associated with increased odds of DFU. Each one-unit increase in BAR corresponded to a 21% higher risk of DFU (OR = 1.21, 95% CI: 1.09–1.35, p < 0.001). In the quartile-based analysis, participants in the highest BAR quartile had a markedly greater risk of DFU than those in the lowest quartile (OR = 3.11, 95% CI: 1.09–8.92, p = 0.035). Restricted cubic spline analysis indicated a non-linear relationship between BAR and DFU risk (p = 0.0127). Subgroup analyses showed that the positive association was generally consistent across strata defined by sex, body mass index, smoking status, and hypertension, with no significant interaction observed (all p for interaction > 0.05). Conclusions: Elevated BAR was independently associated with a higher risk of DFU among diabetic individuals. As an easily accessible composite index reflecting renal function, nutritional status, and systemic inflammatory burden, BAR may help identify diabetic patients who are more likely to develop foot ulceration and may support earlier preventive management.