Association of Charlson comorbidity index with 28- and 90-day mortality in patients with severe acute kidney injury requiring CRRT

Severe acute kidney injury (AKI) requiring continuous renal replacement therapy (CRRT) carries high short‑term mortality. This study evaluated whether the Charlson Comorbidity Index (CCI) independently predicts 28‑ and 90‑day mortality and adds incremental prognostic value beyond established clinical variables. This retrospective study of 1115 adult patients with severe AKI treated with CRRT, CCI was computed at intensive care unit (ICU) admission and categorized (0–1, 2–3, 4–5, ≥6). Primary outcomes were 28‑ and 90‑day mortality. Multivariable Cox proportional hazards models were adjusted for demographics and treatment. Nonlinearity was explored using restricted cubic splines. Robustness was tested using propensity score matching and weighting. The 28‑ and 90‑day mortality rates were 61.3% and 71.1%. A higher CCI was associated with progressively worse survival (log-rank P  < .001). As a continuous variable, CCI correlated with increased mortality after full adjustment (28‑day hazard ratio [HR] per point 1.07, 95% confidence interval [CI] 1.03–1.11; 90‑day HR 1.06, 95% CI 1.03–1.09; P  < .001). CCI cases ≥6 versus 0 to 1 had higher adjusted hazards (28 day HR 1.81; 95% CI 1.40–2.33; 90‑day HR 1.66; 95% CI 1.31–2.10, P  < .001). These findings were consistent across the sensitivity and subgroup analyses. Adding CCI to a base model improved C‑statistics (28‑day 0.759 to 0.775, P  = .002; 90‑day 0.763 to 0.777, P  = .017) and yielded significant net reclassification index/integrated discrimination improvement gains. In severe AKI-CRRT cases, CCI independently predicted 28‑ and 90‑day mortality and modestly improved prognostic discrimination beyond acute severity measures. Routine assessment of CCI may refine early risk stratification, helping prioritize monitoring and supportive interventions for the highest-risk patients.