Early Postoperative Changes in NLR and Serum Creatinine During the First 48 Hours After Cardiac Surgery: A Prospective Exploratory Cohort Study

Background/Objectives: Early changes in serum creatinine after cardiac surgery reflect the interplay of baseline renal vulnerability, cardiopulmonary bypass (CPB), haemodynamic disturbances, perfusion-related factors and systemic inflammation. We examined the postoperative inflammatory response and its associations with serum creatinine during the first 48 h after cardiac surgery. Methods: This prospective single-centre cohort included 88 adults undergoing elective cardiac surgery with CPB. C-reactive protein (CRP), neutrophil-to-lymphocyte ratio (NLR), interleukin-6, interleukin-17A, systemic immune-inflammation index, and systemic inflammatory response index were assessed during the first 48 h. Unadjusted analyses used the absolute change in creatinine from baseline to 48 h. Separate adjusted models used 48-h creatinine as the outcome, including preoperative creatinine and clinical covariates. Results: The measured inflammatory biomarkers showed early postoperative changes. ΔNLR at 48 h had the strongest unadjusted association with Δcreatinine (ρ = 0.334, p = 0.001). ΔNLR and NLR at 48 h remained significant after false-discovery-rate correction. IL-17A detectability increased, although most values were below the assay’s minimum detectable concentration. In adjusted models, ΔNLR (β = 0.00530, 95% CI 0.00103–0.00956; p = 0.016) and NLR (β = 0.00492, 95% CI 0.00061–0.00923; p = 0.026) were associated with 48-h creatinine; other biomarkers were not. Adding ΔNLR increased adjusted R2 by 0.00138 (bootstrap 95% CI −0.00036 to 0.00660). Associations with 24-h NLR were absent after adjustment for 24-h creatinine, and sensitivity estimates excluding eGFR < 30 mL/min/1.73 m2 were imprecise. Conclusions: NLR at 48 h and its change from baseline were associated with postoperative creatinine, but their incremental explanatory contribution was small and uncertain. These exploratory findings do not establish causation, renal specificity, or clinical predictive utility.