Predictive Value of Incorporating Principal Diagnosis into CGA for Short-Term Functional Recovery in an ACE Unit: A Retrospective Study

Purpose: In Acute Care for Elders (ACE) units, Comprehensive Geriatric Assessment (CGA) relies heavily on cumulative comorbidity metrics like Charlson Comorbidity Index (CCI). However, it fails to reflect the dynamic nature of acute illness, limiting its ability to predict short-term functional recovery. Therefore, we aimed to evaluate whether the principal diagnosis, representing acute physiological stress, offers superior predictive value compared to the CCI for functional outcomes in hospitalized older adults. Patients and Methods: This retrospective cohort study included 213 patients (≥ 65 years) admitted to the Acute Care for Elders (ACE) unit between January 2023 and December 2024. The primary outcome was short-term functional recovery, measured as the change in the Barthel Index (BI) from admission to discharge (ΔBI). Hierarchical multiple linear regression was used to create three models: a base model (demographic/clinical covariates), a CCI model, and a principal diagnosis model. Model performance was compared using Adjusted R 2 , Area Under the Curve (AUC) from ROC analysis, Net Reclassification Improvement (NRI), and information criteria (AIC/BIC). Results: The principal diagnosis model demonstrated significantly higher explanatory power (Adjusted R 2 = 0.85) compared to the CCI model (Adjusted R 2 = 0.78) and the base model (Adjusted R 2 = 0.75). The inclusion of principal diagnosis resulted in a significant continuous Net Reclassification Improvement (NRI=0.37, 95% CI 0.11– 0.65, p = 0.006). After adjustment for covariates, specific diagnoses such as Endocrine and Respiratory diseases were strong predictors of recovery, whereas CCI was not statistically significant. Conclusion: The principal diagnosis outperforms cumulative comorbidity as a predictor of short-term functional recovery in the ACE unit. Integrating principal diagnosis into the CGA serves as a valuable and practical complement to refine early functional prognostication. Keywords: functional recovery, aging, hospitalized elderly, clinical decision-making