Comparing Comorbidity Indices to Predict Post-Acute Rehabilitation Outcomes in Older Adults

Objective: Compare 5 comorbidity indices to predict community discharge and functional status following postYacute rehabilitation. Design: This was a retrospective study of Medicare beneficiaries with stroke, lower-extremity fracture, and joint replacement discharged from inpatient rehabilitation in 2011 (N = 105,275). Community discharge and self-care, mobility, and cognitive function were compared using the Charlson, Elixhauser, Tier, Functional Comorbidity, and Hierarchical Condition Category comorbidity indices. Results: Of the patients, 64.4% were female, and 84.6% were non-Hispanic white. Mean age was 79.3 (SD, 7.5) years. Base regression models including sociodemographic and clinical variables explained 56.6%, 42.2%, and 23.0% of the variance (R-2) for discharge self-care; 47.4%, 30.9%, and 18.6% for mobility; and 62.0%, 55.3%, and 37.3% for cognition across the 3 impairment groups. R2 values for self-care, mobility, and cognition increased by 0.2% to 3.3% when the comorbidity indices were added to the models. The base model C statistics for community discharge were 0.58 (stroke), 0.61 (fracture), and 0.62 (joint replacement). The C statistics increased more than 25% with the addition of discharge functional status to the base model. Adding the comorbidity indices individually to the base model resulted in C-statistic increases of 1% to 2%. Conclusion: Comorbidity indices were poor predictors of community discharge and functional status in Medicare beneficiaries receiving inpatient rehabilitation.