Enhanced mortality prediction using frailty models in cardiac surgery patients: evidence from the MIMIC-IV database

The Frailty Index based on Laboratory Tests (FI-Lab) and the Hospital Frailty Risk Score (HFRS) represent two frailty measures, yet their comparative and combined prognostic utility in cardiac surgical populations remains unclear. We conducted a retrospective cohort study using the Medical Information Mart for Intensive Care IV (MIMIC-IV) version 3.1 database, including 4,204 adult patients who underwent cardiac surgery. We evaluated the association of each frailty measure with in-hospital, 28-day, and 1-year mortality and compared the predictive performance of models incorporating FI-Lab, HFRS, or both. Both FI-Lab and HFRS were strongly associated with all mortality endpoints, with FI-Lab consistently providing greater incremental discriminatory value. Adding FI-Lab to the base model increased the AUC from 0.847 to 0.903 for in-hospital mortality, from 0.835 to 0.888 for 28-day mortality, and from 0.780 to 0.827 for 1-year mortality (all p < 0.001), accompanied by significant NRI improvements (range: 0.145–0.214). The combined FI-Lab + HFRS model achieved the highest discrimination (AUC 0.910, 0.892, and 0.836, respectively). FI-Lab and HFRS demonstrated moderate correlation (Spearman ρ = 0.40) and fair categorical agreement (weighted κ = 0.26). FI-Lab and HFRS each capture distinct dimensions of frailty and independently predict postoperative mortality in cardiac surgery patients. Their combination provides superior discrimination. Incorporating both FI-Lab and HFRS into perioperative evaluation may enhance early identification of high-risk individuals and support more individualized postoperative management. Further studies are required before these measures can be recommended for routine perioperative risk assessment.