Neutrophil Percentage-to-Albumin Ratio Predicts Contrast-Induced Acute Kidney Injury in Acute Coronary Syndrome Patients Undergoing Percutaneous Coronary Intervention

<b>Objectives:</b> This study aimed to evaluate the predictive value of the neutrophil percentage-to-albumin ratio (NPAR) and other inflammatory indices for contrast-induced acute kidney injury (CI-AKI) in patients undergoing percutaneous coronary intervention (PCI) for acute coronary syndrome (ACS). <b>Methods:</b> This retrospective cohort study included 317 ACS patients (aged ≥18 years) undergoing PCI between May 2022 and July 2024 at a single center in Turkey. Patients were divided into two groups based on CI-AKI development: those who developed CI-AKI (<i>n</i> = 35, 11.1%) and those who did not (<i>n</i> = 282, 88.9%). Data on demographics, clinical variables, and laboratory parameters (complete blood count, biochemistry) were collected from medical records. Inflammatory indices (neutrophil percentage-to-albumin ratio [NPAR], neutrophil-to-lymphocyte ratio [NLR], systemic immune-inflammation index [SII], pan-immune-inflammation value [PIV], systemic inflammation response index [SIRI]) were calculated. CI-AKI was defined as a ≥0.5 mg/dL absolute or ≥25% relative increase in serum creatinine within 48-72 h after contrast exposure. <b>Results:</b> The CI-AKI group demonstrated significantly higher neutrophil counts (<i>p</i> < 0.001) and neutrophil percentages (<i>p</i> < 0.001) and lower lymphocyte counts (<i>p</i> = 0.024) compared to the non-CI-AKI group. Baseline creatinine was lower in CI-AKI patients (<i>p</i> = 0.001) but showed significantly greater post-procedural increases (<i>p</i> = 0.008). All inflammatory indices predicted CI-AKI development, with NPAR showing superior performance: NPAR (AUC = 0.896, sensitivity 82.9%, specificity 84.0%), NLR (AUC = 0.732), SII (AUC = 0.694), PIV (AUC = 0.674), and SIRI (AUC = 0.709) (all <i>p</i> < 0.001). Independent predictors of CI-AKI included NPAR >18.44 (OR = 8.511, 95% CI: 2.763-26.212, <i>p</i> < 0.001), SIRI > 2.4 × 10³ (OR = 2.991, <i>p</i> = 0.036), neutrophil count (OR = 1.707, <i>p</i> = 0.008), beta-blocker use (OR = 13.037, <i>p</i> = 0.016), and atrial fibrillation (OR = 8.042, <i>p</i> = 0.044). <b>Conclusions:</b> NPAR emerges as an accessible biomarker for predicting CI-AKI in ACS-PCI patients, which is also superior to other inflammation indices. We believe it is necessary to recommend its integration into risk stratification to improve outcomes among PCI recipients.