Association Between Neutrophil-to-Lymphocyte Ratio and Acute Kidney Injury After Cardiac Surgery: A Multicenter Observational Study

Abstract

Introduction: Cardiac surgery-associated acute kidney injury (CSA-AKI) is a frequent complication that increases morbidity, mortality, and resource use. The neutrophil-to-lymphocyte ratio (NLR), derived from a routine complete blood count, is an inexpensive marker of systemic inflammation that may aid early risk stratification. We evaluated the association between perioperative NLR and CSA-AKI in a multicenter cohort of adults undergoing cardiac surgery.

Methods: We conducted a multicenter observational cohort study reported in accordance with the STROBE statement across five cardiac surgery centers in Indonesia. Adults (≥18 years) who underwent cardiac surgery with available complete blood count differentials and perioperative creatinine and urine output monitoring were included. NLR was measured preoperatively, at intensive care unit (ICU) arrival, and on postoperative day 1. The primary outcome was AKI within 7 days, as defined by the KDIGO criteria. Associations were estimated using multivariable mixed-effects logistic regression with a random intercept for the center, prespecified confounder adjustment, restricted cubic splines for non-linearity, propensity score analyses, and multiple imputation.

Results: We analyzed data of 2, 847 patients; CSA-AKI occurred in 24.1% (n=686), of whom 32.4% met KDIGO stages 2–3. Higher perioperative NLR was independently associated with CSA-AKI (adjusted odds ratio 1.71, 95% CI 1.48–1.97 per 1 SD of log-NLR), with consistent estimates across all three measurement windows and in propensity-score analyses. Model discrimination yielded an area under the curve of 0.79 (95% CI 0.77–0.81).

Conclusion: Elevated perioperative NLR was independently associated with CSA-AKI. As a low-cost, routinely available biomarker, NLR may support early identification of high-risk patients pending prospective validation.

Keywords: Neutrophil-to-Lymphocyte Ratio, Acute Kidney Injury, Cardiac Surgery, KDIGO, Inflammation, Risk Stratification