Charlson and Rx-Risk comorbidity indices were predictive of mortality in the Australian health care setting

Objective: To compare the performance of Charlson index and Rx-Risk score using data from Australian Department of Veterans' Affairs.

Study design and setting: A study of older adults (N=94,714) who had both Charlson and Rx-Risk scores based on their hospital diagnoses and prescription medication dispensings during the baseline year (January 2005-December 2005). Predictive ability of 1-year and 3-year mortality was compared by Akaike information criterion model fit statistic and c statistic in logistic regression models. We also compared the scores for identifying specific medical conditions.

Results: Both indices were significant predictors of all-cause mortality (P<0.0001). Of the population identified with a condition from either score, Rx-Risk score identified more than 95% of patients with gastric, respiratory, or cardiovascular condition, compared with Charlson index only identifying 2%, 31%, and 14%, respectively. The indices were comparable regarding diabetes. The Charlson index identified 83% of patients with dementia and 67% of those with cancers, whereas Rx-Risk score identified 38% and 43%, respectively.

Conclusion: Both the Charlson and Rx-Risk scores predict mortality, but neither index identified all comorbidities. Based on data availability, preferences, and research purposes, investigators can use either Charlson index or Rx-Risk score to adjust for comorbidity.