Association of the ISAR Score with Clinical and Operational Outcomes in Older Emergency Department Patients

Background/Objectives: The Identification of Seniors at Risk (ISAR) score is widely used to identify older emergency department (ED) patients at increased risk of adverse outcomes. However, its association with immediate disposition and operational outcomes remains incompletely characterized. This study evaluated the association of ISAR scores with hospital admission and emergency department length of stay (EDLOS). Methods: This retrospective observational cohort study included ED presentations of patients aged ≥65 years at a tertiary university emergency department in 2024. Of 12,105 eligible presentations, 10,090 (83.4%) had a documented ISAR score and constituted the descriptive cohort; 9401 presentations with classifiable admission status were included in the primary admission analysis. Multivariable logistic regression adjusted for age, sex, presenting complaint, triage category, treating specialty, and referral source. The incremental contribution of ISAR beyond routinely available clinical variables was assessed by nested model comparison and receiver operating characteristic analysis. Prolonged EDLOS was defined as ≥6 h. Results: Higher ISAR scores were independently associated with hospital admission and prolonged EDLOS. In the continuous-score admission model, each one-point increase in ISAR was associated with higher odds of admission (OR 1.155, 95% CI 1.121–1.191; p < 0.001), although categorical sensitivity analysis demonstrated a nonlinear association with a plateau at higher scores. ISAR alone showed modest discrimination for admission (AUC 0.589, 95% CI 0.577–0.600). Addition of ISAR to the clinical model increased the AUC from 0.696 to 0.705 (ΔAUC = 0.009, 95% CI 0.005–0.012; p < 0.001). Median EDLOS increased from 326 min (IQR 215–494) at ISAR 0 to 596 min (IQR 324–1312) at ISAR 6. After adjustment including hospital admission status, each one-point increase in ISAR was associated with higher odds of prolonged EDLOS (OR 1.178, 95% CI 1.143–1.214; p < 0.001). Conclusions: Higher ISAR scores were associated with both hospital admission and prolonged EDLOS. ISAR provided statistically significant but modest incremental prognostic information beyond routinely available clinical variables and should be regarded as a geriatric risk-screening tool rather than a stand-alone disposition instrument. Prospective studies are needed to determine whether ISAR-guided clinical pathways improve patient or operational outcomes.