A Multidomain Biomarker Score for Predicting Acute Kidney Injury and Renal Replacement Therapy Initiation in Critically Ill Adults

Background/Objectives: We evaluated the Renal–Inflammatory–Nutritional–Metabolic Index (RIN-IM), a previously published 0–10-point composite biomarker score, for acute kidney injury (AKI) and renal replacement therapy (RRT) initiation in an independent intensive care unit (ICU) cohort. Methods: This retrospective study included 480 adults admitted to two ICUs between October 2023 and August 2026. RIN-IM was calculated within 24 h of admission from creatinine, albumin, systemic immune-inflammation index (platelet count × neutrophil count/lymphocyte count), pan-immune-inflammation value (neutrophil count × platelet count × monocyte count/lymphocyte count), and triglyceride–glucose index (triglyceride and admission glucose concentrations). Patients were classified by RIN-IM Score as low-risk (0–3 points), intermediate-risk (4–6 points), or high-risk (7–10 points). Among patients without AKI or acute RRT initiation at or before the 24-h landmark, subsequent incident AKI was the primary outcome and RRT initiation was the secondary renal outcome. Twenty-eight-day all-cause mortality was evaluated descriptively. Logistic regression and receiver operating characteristic analyses were performed. Results: AKI occurred in 189 patients (39.4%), RRT was initiated in 72 (15.0%), and 157 (32.7%) died within 28 days. In the low-, intermediate-, and high-risk groups, AKI frequencies were 16.0%, 40.0%, and 62.0%; RRT initiation frequencies were 3.3%, 12.2%, and 30.0%; and 28-day mortality was 18.0%, 32.2%, and 48.0%, respectively (all p < 0.001). Adjusted odds ratios per score point was 1.31 (95% confidence interval, 1.16–1.48) for AKI and 1.47 (1.25–1.73) for RRT initiation. Areas under the curve were 0.862 and 0.903, respectively, exceeding those of Acute Physiology and Chronic Health Evaluation II and Sequential Organ Failure Assessment. Conclusions: Higher RIN-IM scores were associated with AKI, RRT initiation, and higher observed 28-day mortality. The score may support early renal risk stratification, pending prospective assessment of calibration and clinical utility.