A combined comorbidity score predicted mortality in elderly patients better than existing scores

Abstract

Objective: To develop and validate a single numerical comorbidity score for predicting short- and long-term mortality, by combining conditions in the Charlson and Elixhauser measures.

Study design and setting: In a cohort of 120,679 Pennsylvania Medicare enrollees with drug coverage through a pharmacy assistance program, we developed a single numerical comorbidity score for predicting 1-year mortality, by combining the conditions in the Charlson and Elixhauser measures. We externally validated the combined score in a cohort of New Jersey Medicare enrollees, by comparing its performance to that of both component scores in predicting 1-year mortality, as well as 180-, 90-, and 30-day mortality.

Results: C-statistics from logistic regression models including the combined score were higher than corresponding c-statistics from models including either the Romano implementation of the Charlson Index or the single numerical version of the Elixhauser system; c-statistics were 0.860 (95% confidence interval [CI]: 0.854, 0.866), 0.839 (95% CI: 0.836, 0.849), and 0.836 (95% CI: 0.834, 0.847), respectively, for the 30-day mortality outcome. The combined comorbidity score also yielded positive values for two recently proposed measures of reclassification.

Conclusion: In similar populations and data settings, the combined score may offer improvements in comorbidity summarization over existing scores.

Figure 1. Number of Citations for Six Seminal Comorbidity Score Papers, 1988 to 2008

This plot displays the number of article citations, for each year between 1988 and 2008, for the papers describing the original Charlson Index [9], its variants [–13], and the original Elixhauser comorbidity classification system [14]. Numbers of citations were obtained from the citing articles feature (restricted to “ARTICLE”) from Web of Science®, ISI Web of Knowledge, Thomson Reuters.

Figure 2. Calibration Curves for the Romano/Charlson Score, the van Walraven/Elixhauser Score, and the Combined Score for Predicting 1-Year Mortality in the Validation Cohort (NJ/PAAD)

Each plot displays the number of patients in the validation cohort having each value of the respective score (columns, left y-axis), the observed proportion (and 95% confidence interval) of deaths in 1-year among patients at a given value (solid line, right y-axis), and the corresponding predicted proportion of death in 1-year (dotted line, right y-axis). Each analysis is age and sex adjusted.