Case-mix factors influence both the selection of dialysis modality and outcomes in end-stage renal disease (ESRD). A detailed characterization of the case-mix differences between peritoneal dialysis (PD) and hemodialysis (HD) patients at the onset of dialysis therapy has not been performed, despite the importance of accounting for baseline differences in future comparisons of outcomes across modality groups. We compared baseline characteristics of 279 PD and 759 HD patients enrolled in the Choices for Healthy Outcomes in Caring for End-Stage Renal Disease (CHOICE) Cohort Study, a prospective study of incident dialysis patients. Comorbidity was assessed using the Index of Coexistent Diseases (ICED), consisting of a medical record review of 19 medical conditions and an observer-based assessment of 11 physical functions. ICED scores range from 0 to 3, with higher levels reflecting more severe comorbidity. Comorbidity was less severe in PD patients than in HD patients: the proportions of patients with ICED 0-1, ICED 2, and ICED 3 were 52%, 26%, and 22%, respectively, among the PD patients and 30%, 39%, and 31%, respectively, among the HD patients (P < 0.001). After controlling for all other factors, the differences in comorbidity remained significant. As compared with patients with ICED 0-1, the odds of being treated with PD for patients with ICED 2 and ICED 3 were less (odds ratio [OR] and 95% confidence intervals) 0.31 (0.17 to 0.56) and 0.50 (0.28 to 0.90), respectively. The number and severity of comorbid conditions at the onset of ESRD is significantly lower in patients choosing PD, independent of other factors influencing modality selection. The increased survival of PD patients reported in recent studies may simply reflect the self- or physician-directed selection of healthier patients to PD. Adjustment for case-mix differences in patients treated with PD versus HD is essential to the assessment of the independent effect of the dialysis modality on outcomes.
Copyright 2002 by the National Kidney Foundation, Inc.