Low serum albumin and elevated blood urea nitrogen-to-albumin and creatinine-to-albumin ratios are associated with mortality in dogs

Objective: To determine whether serum biomarkers, BUN-to-albumin ratio (BAR) and creatinine-to-albumin ratio (CAR), have prognostic utility in dogs. Methods: A retrospective, single-center study utilizing signalment, clinicopathological, and mortality data collected from medical records of dogs presented to a referral hospital from September 2022 through June 2025. Dogs were stratified based on mortality. Results: 327 cases were included. Nonsurvivors (n = 92) had significantly elevated BAR (median, 6.62; 95% CI, 5.69 to 7.61) and CAR (0.36; 95% CI, 0.32 to 0.42) compared with survivors at 5.01 (95% CI, 4.52 to 5.50) and 0.29 (95% CI, 0.27 to 0.31), respectively. Nonsurvivors had lower albumin (2.9 g/dL; 95% CI, 2.7 to 3.0) than survivors (3.2 g/dL; 95% CI, 3.1 to 3.2). Blood urea nitrogen was higher in nonsurvivors (18.8 mg/dL; 95% CI, 17.1 to 23.2) than survivors (16.0 mg/dL; 95% CI, 14.8 to 17.4). Survival analysis identified low albumin as the strongest predictor of mortality, with increased risk of death (hazard ratio, 2.01; CI, 1.32 to 3.07). High BAR, BUN, and CAR were associated with poor survival, whereas creatinine was not related to outcome. A random forest-classified model showed strong discrimination between survivors and nonsurvivors, with an area under the curve of 0.998 (Specificity, 100%; Sensitivity, 71.7%). Conclusions: Nonsurvivors had significantly higher BAR, CAR, BUN, and creatinine and lower albumin; BAR, CAR, BUN, and albumin outperformed creatinine in predicting mortality. Clinical Relevance: Biochemical ratios are easily calculated, have the potential to predict mortality in dogs, and thus warrant further investigation.