Association between postoperative creatinine-to-WBC ratio and one-year mortality following coronary artery bypass grafting: an exploratory retrospective cohort study

Both renal dysfunction and systemic inflammation contribute to adverse outcomes following coronary artery bypass grafting (CABG). This study evaluated the association between the postoperative creatinine-to-white blood cell ratio (Cr/WBC) and 1-year all-cause mortality after CABG, exploring whether this composite metric offers complementary epidemiological insights over standalone parameters. We analyzed 6,553 adult patients undergoing first-time CABG from the MIMIC-IV database. The primary exposure was the log-transformed post-ICU admission Cr/WBC ratio [ln(Cr/WBC)]. Multivariable Cox proportional hazards regression, restricted cubic spline (RCS), causal mediation, and receiver operating characteristic (ROC) analyses were performed to evaluate risk gradients, subgroup consistency, and discriminatory power for 1-year mortality. Overall 1-year mortality was 4.60% ( n = 303). In fully adjusted Cox models, each 1-unit increase in ln(Cr/WBC) was associated with an 81.6% increase in 1-year mortality risk (adjusted HR = 1.816, 95% CI: 1.575–2.094, P < 0.001). Patients in the highest quartile (Q4) exhibited significantly higher mortality than those in Q1 (adjusted HR = 2.600, P < 0.001). Subgroup associations remained statistically significant in patients with chronic kidney disease, acute myocardial infarction, and hypertension. RCS analysis demonstrated a progressive non-linear risk elevation(P non−linearity = 0.029). However, multivariable comparative modeling and causal mediation analysis indicated that the prognostic signal was overwhelmingly driven by serum creatinine, with WBC count providing negligible direct or mediating effects ( P = 0.658). Furthermore, standalone serum creatinine showed significantly superior discriminatory performance over the composite ratio (AUC: 0.7393 vs. 0.6929, P < 0.001). Postoperative ln(Cr/WBC) is significantly associated with 1-year mortality after CABG, but this signal is predominantly governed by renal impairment rather than leucocyte counts. Rather than proposing the ratio as a novel clinical tool for risk stratification, our study provides an integrative framework to explore post-operative renal-inflammatory dynamics in epidemiological research. Not applicable.