Comparing Performance of Comorbidity Indices in Predicting Functional Status, Health-Related Quality of Life, and Total Health Care Use in Older Adults With Back Pain.

Abstract

Secondary analysis of prospective cohort study. Common comorbidity indices were developed to predict mortality and may not be optimal for functional outcomes. Determine how well the Functional Comorbidity Index (FCI) predicts outcomes in older adults with back pain versus the Quan/Charlson and Elixhauser comorbidity indices. We included 5155 adults ≥65 years with new primary care visits for back pain. Comorbidity was measured using diagnosis codes 12 months prior to the new visit. Outcomes of functional limitation (Roland Morris Disability Questionnaire [RMDQ]), health-related quality-of-life (EQ5D), and total health care use (sum of Relative Value Units [RVUs]) were measured 12 months the new visit. We compared multivariable models containing preselected prognostic factors. Spearman's Correlation Coefficients among the indices were ≥0.70. Multivariable models for RMDQ had similar R2 and mean squared error (MSE) of prediction when using the FCI (R²=0.190; MSE= 6.19), Quan/Charlson (R²=0.184; MSE=6.20), or Elixhauser (R²=0.189; MSE=6.19). Multivariable models for EQ5D showed small differences in R² and MSE when using the FCI (R²=0.157; MSE= 0.163), Quan/Charlson (R²=0.148; MSE=0.164), or Elixhauser (R²=0.154; MSE=0.163). Multivariable models for health care use had similar Akaike's information criterion (AICs) when using the FCI (AIC=10.04), Quan/Charlson (AIC=10.04), or Elixhauser (AIC=10.01). All indices performed similarly in predicting outcomes. There does not seem to be an advantage to using one index over another for older adults with back pain. There is still a need to develop better function-based risk adjustment models that improve prediction of functional outcomes versus standard comorbidity indices. Level 2 Prognostic Evidence. <i>J Orthop Sports Phys Ther, Epub 23 Jul 2019. doi:10.2519/jospt.2019.8764</i>.