Peritoneal and hemodialysis: I. Differences in patient characteristics at initiation.

BACKGROUND: Comparisons of mortality outcomes between peritoneal dialysis (PD) and hemodialysis (HD) patients have shown varying results, which may be caused by the unequally distributed clinical conditions of patients at initiation. To address this issue, we evaluated the clinical characteristics of 105,954 patients at the initiation of PD and HD, using the U.S. national incidence data on treated end-stage renal disease from the Medical Evidence Form, 1995 to 1997. METHODS: A general linear model was used to analyze differences of age, albumin, creatinine, blood urea nitrogen (BUN), and hematocrit; categorical data analysis to evaluate body mass index (BMI), grouped into four categories: < 19, 19-25 (< 25), 25-30 (< 30), and 30+; and logistic regression to assess the likelihood of initiating PD versus HD. Diabetics (DM) were analyzed separately from non-diabetics (NDM). Explanatory variables in the logistic regression included incidence year, race, gender, age, BMI, albumin, creatinine, BUN, and hematocrit. Race included white and black. Age was categorized into four groups: 20-44, 45-64, 65-74, and 75+. RESULTS: At the initiation of dialysis PD patients were approximately 6 years younger (P < 0.0001) than HD patients. PD patients also had higher (P < 0.0001) albumin (+0.35 g/dL for DM and +0.23 g/dL for NDM) and hematocrit (+1.64% for DM and +1.71% for NDM) levels, and lower (P < 0.04) BUN (-8.75 mg/dL for DM and -5.24 mg/dL for NDM) and creatinine (-0.51 mg/dL for DM and -0.23 mg/dL for NDM) levels than HD patients. Whites had a higher (P < 0.0001) likelihood of starting PD than blacks, and patients with BMI <19 had a lower (P < 0.0001) chance of beginning on PD. CONCLUSION: PD patients had favorable clinical conditions at the initiation of dialysis, which should be taken into consideration when comparing dialysis outcomes between the two modalities.

Peritoneal and hemodialysis: II. Mortality risk associated with initial patient characteristics.

BACKGROUND: Patients initiating with peritoneal dialysis (PD) have favorable clinical conditions compared with hemodialysis (HD) patients, which may contribute to the varying results found in studies of mortality across the two therapies. METHODS: National incidence data of end-stage renal disease patients from 1995 to 1997 were used, excluding the first 90 days of treatment and including all patients who were on either PD or HD on day 91. Patients were then followed for a one-year period. A Cox proportional hazards regression analysis was used, separating diabetics and non-diabetics, and two statistical models were applied. Model 1 included race, gender, age, initial modality, and incidence year as explanatory variables. Model 2 added body mass index (BMI), initial levels of serum albumin, creatinine, and blood urea nitrogen. RESULTS: Age was most highly associated with mortality, followed by biochemical variables, BMI, gender, and dialysis modality. In diabetics, the hazard ratio (HR) from Model 1 indicated no difference [1.046, 95% confidence limits (CL) 0.989-1.105; P> 0.1, HD was the reference] in mortality between PD and HD, while Model 2 demonstrated that PD patients had a 13.4% (1.134, CL 1.072-1.100, P < 0.0001) higher chance of death. In non-diabetics, hazard ratios (HRs) from Models 1 and 2 indicated that PD patients had a 23.5% (0.765, 0.722-0.812, P < 0.0001) and 11.9% (0.881, 0.30-0.935, P < 0.0001), respectively, lower likelihood of death than HD patients. CONCLUSION: Our study indicates that the results changed depending on the analytical methods used. We recommend that, due to the unequally distributed clinical conditions of patients at initiation, comparisons of mortality outcomes between dialysis modalities should be made with caution.