Retrospective Cohort Study on the Association Between a Laboratory Test-Derived Frailty Index and Mortality in Elderly Critically Ill Patients With Chronic Kidney Disease

BACKGROUND/AIMS: Chronic kidney disease (CKD) represents a growing worldwide health concern. There is a need for easily obtainable markers that can improve risk evaluation in affected patients. Here, we investigated whether a laboratory-derived frailty index (FI-Lab) carries prognostic information for older CKD individuals admitted to intensive care. METHODS: A retrospective cohort design was adopted, drawing on the MIMIC-IV repository. Records of elderly ICU patients with diagnosed CKD were retrieved. The endpoints of interest were all-cause death within 30 and 90 days. Cox proportional hazards regression with incremental covariate adjustment and propensity score matching were employed to quantify the independent contribution of FI-Lab to survival. RESULTS: The analytic sample consisted of 5013 hospitalized CKD patients (mean age 77.9 ± 7.6 years; 61.4% male). Following full adjustment, a 0.1-unit rise in FI-Lab corresponded to a 94% higher mortality risk at 30 days (HR 1.94; 95% CI 1.57-2.40) and a 65% higher risk at 90 days (HR 1.65; 95% CI 1.43-1.91; both p < 0.001). Propensity-matched analyses yielded comparable estimates. No meaningful association emerged between FI-Lab and ICU or hospital length of stay. Conversely, higher FI-Lab values were accompanied by greater odds of acute kidney injury and continuous renal replacement therapy utilization. CONCLUSIONS: An elevated FI-Lab score at ICU entry is independently tied to elevated short- and intermediate-term mortality in older critically ill patients with CKD. Confirmatory prospective work is needed to establish its clinical role in this population.