Adapting the Charlson Comorbidity Index for use in patients with ESRD

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.

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.

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.

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.