Age-Normalized Baseline Renal Function: A Simple Risk Marker in Coronary Artery Bypass Grafting

Objective: Creatinine-based estimated glomerular filtration rate (eGFR) equations incorporate age but do not normalize renal function to age-expected values. We evaluated whether the eGFR-to-Age ratio is associated with outcomes after isolated coronary artery bypass grafting (CABG). Methods: This single-center retrospective cohort included 1311 patients. Multivariable and Firth penalized logistic regression, DeLong receiver operating characteristic (ROC) comparisons, bootstrap internal validation, and outcome-specific Youden cut-offs were used. Results: Thirty-day mortality occurred in 19 (1.4%) and postoperative dialysis in 17 (1.3%) patients. After adjustment, each 0.1-unit increase in the ratio was associated with lower odds of mortality, with odds ratio (OR) 0.786, 95%; confidence interval (CI) 0.679-0.915, and dialysis (OR 0.735, 95% CI 0.633-0.851). For mortality, discrimination of the ratio (AUC 0.818) was comparable to that of eGFR and age entered separately (AUC 0.831, p = 0.195) and higher than that of eGFR alone (AUC 0.767, p = 0.005) and European System for Cardiac Operative Risk Evaluation (EuroSCORE) II (AUC 0.722, p = 0.018). Negative predictive values exceeded 99%, largely reflecting low event rates, whereas positive predictive values were below 5%. Conclusions: The eGFR-to-Age ratio is a simple single-parameter summary of eGFR and age, with discrimination comparable to that of its two components. It may serve as a supplementary bedside screening parameter rather than a replacement for comprehensive risk scores, pending external validation.