title: Examining the Association Between Comorbidity Indexes and Functional Status in Hospitalized Medicare Fee-for-Service Beneficiaries.
abstract: BACKGROUND
  Medicare 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.
  
  
  OBJECTIVE
  The 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).
  
  
  METHODS
  This was a retrospective cohort study.
  
  
  METHODS
  Medicare 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.
  
  
  RESULTS
  Base 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%).
  
  
  CONCLUSIONS
  Patients from 3 impairment categories were included in the sample.
  
  
  CONCLUSIONS
  The 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.
authors.affiliation: 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.
authors.forename: Amit
authors.initials: A
authors.lastname: Kumar
authors.affiliation: J.E. Graham, PhD, DC, Division of Rehabilitation Sciences, University of Texas Medical Branch.
authors.forename: James E
authors.initials: JE
authors.lastname: Graham
authors.affiliation: L. Resnik, PT, PhD, Department of Health Services, Policy and Practice, Brown University, Providence, Rhode Island, and Providence VA Medical Center, Providence, Rhode Island.
authors.forename: Linda
authors.initials: L
authors.lastname: Resnik
authors.affiliation: A.M. Karmarkar, PhD, MPH, Division of Rehabilitation Sciences, University of Texas Medical Branch.
authors.forename: Amol M
authors.initials: AM
authors.lastname: Karmarkar
authors.affiliation: A. Deutsch, RN, PhD, CRRN, RTI International, Washington, DC, and Rehabilitation Institute of Chicago, Chicago, Illinois.
authors.forename: Anne
authors.initials: A
authors.lastname: Deutsch
authors.affiliation: A. Tan, MD, PhD, Institute for Translational Sciences, University of Texas Medical Branch.
authors.forename: Alai
authors.initials: A
authors.lastname: Tan
authors.affiliation: S. Al Snih, MD, PhD, Division of Rehabilitation Sciences, University of Texas Medical Branch, and Sealy Center on Aging, University of Texas Medical Branch.
authors.forename: Soham
authors.initials: S
authors.lastname: Al Snih
authors.affiliation: K.J. Ottenbacher, PhD, OTR, Division of Rehabilitation Sciences, University of Texas Medical Branch, and Sealy Center on Aging, University of Texas Medical Branch.
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Ottenbacher
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019643:Arthroplasty, Replacement / Q000534:rehabilitation*; D015897:Comorbidity; D004185:Disability Evaluation; D018588:Fee-for-Service Plans / Q000706:statistics & numerical data*; D005260:Female; D050723:Fractures, Bone / Q000534:rehabilitation*; D006302:Health Services Research; D006801:Humans; D007297:Inpatients / Q000706:statistics & numerical data*; D007869:Leg Injuries / Q000534:rehabilitation*; D008297:Male; D006278:Medicare / Q000191:economics* / Q000706:statistics & numerical data; D012047:Rehabilitation Centers / Q000706:statistics & numerical data*; D012189:Retrospective Studies; D000071939:Stroke Rehabilitation; D014481:United States