Comparison of the Clinical Frailty Scale and the FRAIL Scale for predicting short-term outcomes in older adults hospitalized with infectious diseases: a multicentre prospective study

Background Frailty is a major determinant of adverse health outcomes in older adults, yet evidence comparing commonly used frailty instruments in patients hospitalized with infectious diseases is limited. We aimed to compare the prognostic performance of the Clinical Frailty Scale (CFS) and the FRAIL Scale for predicting short-term outcomes in older adults admitted to infectious diseases departments. Methods This prospective multicentre observational cohort study included adults aged ≥ 65 years hospitalized in infectious diseases departments across 16 hospitals in Türkiye. Frailty was rated at enrolment, during acute illness, using the CFS (frail: ≥5) and the FRAIL Scale (frail: ≥3). The primary outcome was a composite poor 28-day outcome, defined by day-28 status as being in the intensive care unit, ongoing general-ward hospitalization, or death within 28 days. Separate multivariable logistic regression models using the same covariates and receiver operating characteristic (ROC) analyses were used to compare the two instruments. Results Among 151 older adults, 102 (67.5%) were classified as frail by the FRAIL Scale and 87 (57.6%) by the CFS. Poor 28-day outcome occurred in 18 patients (11.9%). It was more frequent among CFS-defined frail than non-frail patients (18.4% vs. 3.1%, p = 0.004), whereas the difference by FRAIL classification was not statistically significant (15.7% vs. 4.1%, p = 0.058). After adjustment for age, sex, and polypharmacy, CFS-defined frailty was associated with higher odds of poor 28-day outcome (adjusted OR 5.99, 95% CI 1.26–28.42; p = 0.024), whereas FRAIL-defined frailty was not significantly associated with the outcome (adjusted OR 3.63, 95% CI 0.76–17.41; p = 0.107). The CFS showed an AUC of 0.823 (95% CI 0.702–0.944), compared with 0.696 (95% CI 0.579–0.813) for the FRAIL Scale; the difference between the AUCs was statistically significant (DeLong p = 0.034). Conclusions In this cohort, CFS ratings obtained during acute hospitalization showed higher discrimination for poor 28-day outcome than the FRAIL Scale and remained associated with the outcome after adjustment for age, sex, and polypharmacy. Given the limited number of events and assessment during acute illness rather than for pre-illness status, these findings should be interpreted cautiously, may not apply directly to standard pre-illness CFS assessment, and require validation in larger cohorts.