American Journal of Epidemiology Practice of Epidemiology Updating and Validating the Charlson Comorbidity Index and Score for Risk Adjustment in Hospital Discharge Abstracts Using Data from 6 Countries

With advances in the effectiveness of treatment and disease management, the contribution of chronic comorbid diseases (comorbidities) found within the Charlson comorbidity index to mortality is likely to have changed since development of the index in 1984. The authors reevaluated the Charlson index and reassigned weights to each condition by identifying and following patients to observe mortality within 1 year after hospital discharge. They applied the updated index and weights to hospital discharge data from 6 countries and tested for their ability to predict in-hospital mortality. Compared with the original Charlson weights, weights generated from the Calgary, Alberta, Canada, data (2004) were 0 for 5 comorbidities, decreased for 3 comorbidities, increased for 4 comorbid-ities, and did not change for 5 comorbidities. The C statistics for discriminating in-hospital mortality between the new score generated from the 12 comorbidities and the Charlson score were 0.825 (new) and 0. The updated index of 12 comorbidities showed good-to-excellent discrimination in predicting in-hospital mortality in data from 6 countries and may be more appropriate for use with more recent administrative data. The Charlson comorbidity index (1), a method of predicting mortality by classifying or weighting comorbid conditions (comorbidities), has been widely utilized by health researchers to measure burden of disease and case mix. Since the publication of Charlson et al.'s original article in 1987 (1), the paper has been cited nearly 5,500 times, and the index has been validated for its ability to predict mortality in various disease subgroups, including cancer, renal disease, stroke, intensive care, and liver disease (2–8). These studies consistently demonstrate that the Charlson index is a valid prognostic indicator for mortality. In 1984, Charlson et al. defined the clinical conditions to be included in the index after a review of 559 hospital charts for patients admitted to medical services at 1 hospital and then assessed the association of these comorbidities with 1-year all-cause mortality (1). Among many potential comor-bidity variables assessed, 17 were found to be associated with 1-year mortality. To measure disease burden, Charlson et al. assigned a weighted score to each comorbid condition based on the relative risk of 1-year mortality. After validating the index in breast cancer patients, Charlson et al. reported that the score as an indicator of disease burden had a strong ability to predict mortality (1). To apply the index in administrative hospital discharge data, Deyo et al. (9), Romano et al. (10), and D'Hoore …