Frailty Index Laboratory (FI-Lab) as predictor of poor outcomes for intra-hospital multidrug-resistant Klebsiella pneumoniae bloodstream infections: a single-centre retrospective cohort study

Background and objectives Bloodstream infections (BSIs) caused by carbapenemase-resistant Klebsiella pneumoniae (CR-Kp) are associated with high morbidity and mortality, particularly in frail patients. Identifying frailty upon hospital admission may improve clinical decision-making and outcomes. This study evaluates the Frailty Index Laboratory (FI-Lab) as a predictive tool for adverse outcomes in patients with CR-Kp BSIs. Methods This retrospective cohort study was conducted between January 2020 and September 2024 at the Policlinico Universitario di Bari. Frailty was assessed using FI-Lab, derived from 35 laboratory parameters measured within 96 h of admission. Outcomes included all-cause mortality, 28 day mortality and relapse, with FI-Lab predictive accuracy evaluated via ROC curve analysis. Results A total of 182 patients with CR-Kp BSIs were included, of whom 48 died (26.3%). Non-survivors had significantly higher FI-Lab scores than survivors (0.66 ± 0.10 versus 0.33 ± 0.16, P < 0.0001). FI-Lab demonstrated excellent predictive accuracy for mortality (AUC = 0.94), 28 day mortality (AUC = 0.87) and relapse (AUC = 0.87). Each 0.10-point increase in FI-Lab was associated with a higher risk of mortality (HR = 2.07), 28 day mortality (HR = 1.86) and relapse (HR = 1.52). Conclusions The FI-Lab proved to be a simple and robust tool for early frailty assessment in patients with CR-Kp BSIs. Further studies are needed to validate these findings and explore the broader applicability of FI-Lab in managing infections in vulnerable populations.