Frailty and Hospitalization After Emergency Department Evaluation Within Triage Categories in Older Patients: A Retrospective Cohort Study

OBJECTIVES: Triage reflects acute urgency, whereas frailty may also influence disposition in older emergency department (ED) patients. This study aimed to estimate the association between Clinical Frailty Scale (CFS)-defined frailty and hospitalization after ED evaluation within Japan Triage and Acuity Scale (JTAS) categories and assess whether the strength varied across triage categories. METHODS: We conducted a single-center retrospective cohort study in an urban tertiary hospital in Japan. We identified consecutive triaged ED visits by patients aged ≥ 65 years from November 2025 to March 2026. Visits with CFS scores and covariates constituted the complete-case cohort. CFS ≥ 5 was defined as frailty. The primary outcome was admission to the study hospital or acute-care interhospital transfer. We used a mixed-effects logistic regression model with a CFS-by-JTAS interaction term, adjusting for age, sex, mode of arrival, injury- or poisoning-related visit, living arrangement, and long-term care needs certification, with patient-level random intercept. The global interaction was assessed using a likelihood-ratio test. RESULTS: Among 3127 ED visits, 1526 resulted in hospitalization. In JTAS 1, the adjusted odds ratio (OR) for CFS ≥ 5 was not estimated because of quasi-complete separation. In the model excluding JTAS 1, the adjusted OR was 1.00 (95% confidence interval [CI], 0.65-1.55) in JTAS 2, 1.54 (95% CI: 1.19-1.99) in JTAS 3, and 2.01 (95% CI: 1.13-3.58) in JTAS 4/5. The global CFS-by-JTAS interaction was not statistically significant (P for interaction = 0.091). CONCLUSIONS: Category-specific estimates suggested little association in JTAS 2 but were numerically larger in JTAS 3 and JTAS 4/5. However, the global interaction was nonsignificant, providing insufficient evidence that the association differed across categories. Prospective studies should examine the clinical, geriatric, social, decision-related, and healthcare-system factors that may underlie this association among older patients with comparable triage-assessed urgency.