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Practical considerations on the use of the Charlson comorbidity index with administrative data bases
W D'Hoore1, A Bouckaert, C Tilquin
1Université de Montréal, Départment d'Administration de la Santé, Equipe de Recherche Opérationnelle en Santé, Montréal, Canada.
Insights
The Charlson comorbidity index, adapted for ICD-9 codes, effectively predicts inpatient death in ischemic heart disease patients. This validated index aids risk adjustment in administrative databases.
Area of Science:
- Health Services Research
- Epidemiology
- Biostatistics
Background:
- Assessing the burden of comorbid disease is crucial for patient outcomes.
- Administrative databases offer valuable data for health services research.
- Existing comorbidity measures may require adaptation for specific data sources.
Purpose of the Study:
- To adapt the Charlson comorbidity index for use with International Classification of Disease (ICD-9) codes.
- To evaluate the index's ability to predict inpatient death in patients with ischemic heart disease.
- To assess the index's utility for risk adjustment in administrative data.
Main Methods:
- Adapted the Charlson index using ICD-9 codes from the MED-ECHO database.
- Applied multiple logistic regression to analyze predictors of inpatient death.
- Examined various transformations of the comorbidity score for predictive accuracy.
- Validated the index on independent MED-ECHO data from 1990-1991.
Main Results:
- The adapted comorbidity index was strongly and consistently associated with inpatient death.
- Transforming the index into four dummy variables yielded the best predictive accuracy (AUC = 0.87).
- Validation analysis confirmed the index's statistical properties in a separate cohort.
Conclusions:
- The adapted Charlson index is an efficient tool for risk adjustment using administrative data.
- The index demonstrates strong predictive value for inpatient mortality in ischemic heart disease.
- Further testing on other conditions is recommended to broaden its applicability.
Abstract:
To develop a measure of the burden of comorbid disease from the MED-ECHO data base (Québec), the so-called Charlson index was adapted to International Classification of Disease (ICD-9) codes. The resulting comorbidity index was applied to the study of inpatient death in 33,940 patients with ischemic heart disease. Multiple logistic regression was used to relate inpatient death to its predictors, including gender, principal diagnosis, age, and the comorbidity index. Various transformations of the comorbidity score were performed, and their effect on the predictive accuracy was assessed. The comorbidity index was constantly and strongly associated with death. From a statistical viewpoint, the best results were obtained when the index was transformed into four dummy independent variables (the area under the receiver-operating curve is then 0.87). In a validation analysis performed on 1990-1991 MED-ECHO data (36,012 admissions with ischemic heart disease), the comorbidity index has the same statistical properties. We conclude that the Charlson index may be an efficient approach to risk adjustment from administrative data bases, although it should be tested on other conditions.