Original investigation: dialysis therapy
Adapting the charlson comorbidity index for use in patients with ESRD

https://doi.org/10.1016/S0272-6386(03)00415-3Get rights and content

Abstract

Background:

Accurate prediction of survival for patients with end-stage renal disease (ESRD) and multiple comorbid conditions is difficult. In nondialysis patients, the Charlson Comorbidity Index has been used to adjust for comorbidity. The purpose of this study is to assess the validity of the Charlson index in incident dialysis patients and modify the index for use specifically in this patient population.

Methods:

Subjects included all incident hemodialysis and peritoneal dialysis patients starting dialysis therapy between July 1, 1999, and November 30, 2000. These 237 patients formed a cohort from which new integer weights for Charlson comorbidities were derived using Cox proportional hazards modeling. Performance of the original Charlson index and the new ESRD comorbidity index were compared using Kaplan-Meier survival curves, change in likelihood ratio, and the c statistic.

Results:

After multivariate analysis and conversion of hazard ratios to index weights, only 6 of the original 18 Charlson variables were assigned the same weight and 6 variables were assigned a weight higher than in the original Charlson index. Using Kaplan-Meier survival curves, we found that both the original Charlson index and the new ESRD comorbidity index were associated with and able to describe a wide range of survival. However, the new study-specific index had better validated performance, indicated by a greater change in the likelihood ratio test and higher c statistic.

Conclusion:

This study indicates that the original Charlson index is a valid tool to assess comorbidity and predict survival in patients with ESRD. However, our modified ESRD comorbidity index had slightly better performance characteristics in this population.

Section snippets

Data source and patient selection

The Southern Alberta Renal Program (SARP) provides care to all patients with ESRD in the southern portion of Alberta, Canada. A computerized database of all predialysis, dialysis, and kidney transplantation patients in this catchment area of 1.3 million people is maintained by SARP20 and was used to identify study subjects. The province of Alberta overall has a population of approximately 2.8 million persons, of whom 10% identify themselves as ethnic minorities (3.5%, Chinese ethnicity; 2%,

Results

Table 1 lists characteristics of the 237 incident patients with ESRD. The majority of subjects were men, with a mean age of 62.5 years. The mortality rate for the study period was 23.6%. In terms of modality, 77.6% of subjects were on hemodialysis therapy, with the remaining 22.4% on peritoneal dialysis therapy. Primary causes of ESRD in this population were diabetes, glomerulonephritis, and hypertension/ischemic nephropathy.

The original Charlson comorbidity score and new ESRD comorbidity

Discussion

In this study, we evaluated the ability of the Charlson Comorbidity Index to predict survival in a population of incident patients with ESRD, and developed a new ESRD comorbidity index specific for dialysis patients based on original Charlson Comorbidity Index variables. Results suggest that the original Charlson index is a valid tool to assess comorbidity and predict survival in this dialysis population. Further validation in a separate data set is needed to acquire more information on the

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Supported in part by the Alberta Heritage Foundation for Medical Research; Health Research Fund Center for Advancement of Health, Calgary Health Region; a Government of Canada Research Chair (W.A.G.); and a Health Scholar Award from the Alberta Heritage Foundation for Medical Research (W.A.G.).

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