Impact of prognostic nutritional index on mortality among patients receiving coronary artery bypass grafting surgery: a retrospective cohort study

Background The Prognostic Nutritional Index (PNI), calculated from serum albumin levels and lymphocyte counts, is a simple and objective measure of nutritional status. While PNI has been shown to be a significant prognostic tool in gastrointestinal surgery and heart failure, its role in patients undergoing coronary artery bypass grafting (CABG) remains unclear. This study aims to evaluate whether PNI can serve as a meaningful risk factor for patients undergoing CABG. Methods This observational retrospective analysis involved a substantial sample of 2889 patients who underwent isolated CABG at one of four medical centres. The primary outcomes included short- and long-term mortality. Perioperative serum albumin levels and total lymphocyte counts used to calculate PNIs were collected 48 hours before the operation, 24 hours after the operation and at discharge. Univariate and multivariate logistic regression analyses were conducted to identify the risk factors of short-term mortality. Survival and relative risks were assessed using Cox regression analysis and the Kaplan-Meier test. Results Among the 2889 patients, 64 (2.2%) died within 30 days following CABG. Multivariate logistic regression revealed that higher preoperative PNI was independently associated with reduced short-term mortality (OR=0.852 per unit increase, 95% CI 0.802 to 0.904, p<0.001). Regarding long-term outcomes, among the 2825 patients who were discharged alive, 199 deaths occurred over a median follow-up period of 54.9 months. Patients with a normal PNI at discharge (>40) exhibited significantly higher long-term survival rates compared with those with a lower PNI (≤40) (log-rank p=0.003). Multivariate Cox regression analysis confirmed that a normal PNI at discharge(>40) independently predicted a lower risk of long-term all-cause mortality (HR=0.718, 95% CI 0.529 to 0.974, p=0.033). Conclusions PNI at various time points may play a crucial predictive role in mortality among CABG-treated patients, and a low PNI serves as a risk factor for both short- and long-term survival.