• Amit Kumar, James E Graham, Linda Resnik, Amol M Karmarkar, Anne Deutsch, Alai Tan, Soham Al Snih, and Kenneth J Ottenbacher.
• A. Kumar, PT, MPH, PhD, Division of Rehabilitation Sciences, University of Texas Medical Branch, 301 University Blvd, Rte 1137, Galveston, TX 77555-1137 (USA). amkumar@utmb.edu.
• Phys Ther. 2016 Feb 1; 96 (2): 232-40.

BackgroundMedicare data from acute hospitals do not contain information on functional status. This lack of information limits the ability to conduct rehabilitation-related health services research.ObjectiveThe purpose of this study was to examine the associations between 5 comorbidity indexes derived from acute care claims data and functional status assessed at admission to an inpatient rehabilitation facility (IRF). Comorbidity indexes included tier comorbidity, Functional Comorbidity Index (FCI), Charlson Comorbidity Index, Elixhauser Comorbidity Index, and Hierarchical Condition Category (HCC).DesignThis was a retrospective cohort study.MethodsMedicare beneficiaries with stroke, lower extremity joint replacement, and lower extremity fracture discharged to an IRF in 2011 were studied (N=105,441). Data from the beneficiary summary file, Medicare Provider Analysis and Review (MedPAR) file, and Inpatient Rehabilitation Facility-Patient Assessment Instrument (IRF-PAI) file were linked. Inpatient rehabilitation facility admission functional status was used as a proxy for acute hospital discharge functional status. Separate linear regression models for each impairment group were developed to assess the relationships between the comorbidity indexes and functional status. Base models included age, sex, race/ethnicity, disability, dual eligibility, and length of stay. Subsequent models included individual comorbidity indexes. Values of variance explained (R(2)) with each comorbidity index were compared.ResultsBase models explained 7.7% of the variance in motor function ratings for stroke, 3.8% for joint replacement, and 7.3% for fracture. The R(2) increased marginally when comorbidity indexes were added to base models for stroke, joint replacement, and fracture: Charlson Comorbidity Index (0.4%, 0.5%, 0.3%), tier comorbidity (0.2%, 0.6%, 0.5%), FCI (0.4%, 1.2%, 1.6%), Elixhauser Comorbidity Index (1.2%, 1.9%, 3.5%), and HCC (2.2%, 2.1%, 2.8%).LimitationPatients from 3 impairment categories were included in the sample.ConclusionsThe 5 comorbidity indexes contributed little to predicting functional status. The indexes examined were not useful as proxies for functional status in the acute settings studied.© 2016 American Physical Therapy Association.

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