Body mass index, dialysis modality, and survival: analysis of the United States Renal Data System Dialysis Morbidity and Mortality Wave II Study.

BACKGROUND: The impact of obesity on survival in end-stage renal disease (ESRD) patients as related to dialysis modality (i.e., a direct comparison of hemodialysis with peritoneal dialysis) has not been assessed adjusting for differences in medication use, follow-up > or =2 years, or accounting for changes in dialysis modality. METHODS: We performed a retrospective cohort study of the United States Renal Data System (USRDS) Dialysis Morbidity and Mortality Wave II Study (DMMS) patients who started dialysis in 1996, and were followed until October 31 2001. Cox regression analysis was used to model adjusted hazard ratios (AHR) for mortality for categories of body mass index (BMI), both as quartiles and as > or =30 kg/m2 vs. lower. Because such a large proportion of peritoneal dialysis patients changed to hemodialysis during the study period (45.5%), a sensitivity analysis was performed calculating survival time both censoring and not censoring on the date of change from peritoneal dialysis to hemodialysis. RESULTS: There were 1675 hemodialysis and 1662 peritoneal dialysis patients. Among hemodialysis patients, 5-year survival for patients with BMI > or =30 kg/m2 was 39.8% vs. 32.3% for lower BMI (P < 0.01 by log-rank test). Among peritoneal dialysis patients, 5-year survival for patients with BMI >/=30 kg/m2 was 38.7% vs. 40.4% for lower BMI (P > 0.05 by log-rank test). In adjusted analysis, BMI > or = 30 kg/m2 was associated with improved survival in hemodialysis patients (AHR 0.89; 95% CI 0.81, 0.99; P= 0.042) but not peritoneal dialysis patients (AHR = 0.99; 95% CI, 0.86, 1.15; P= 0.89). Results were not different on censoring of change from peritoneal dialysis to hemodialysis. CONCLUSION: We conclude that any survival advantage associated with obesity among chronic dialysis patients is significantly less likely for peritoneal dialysis patients, compared to hemodialysis patients.

Body mass index and enrollment on the renal transplant waiting list in the United States.

BACKGROUND: Previous studies of body mass index (BMI) and enrollment on the renal transplant waiting list have not analyzed a national population of chronic dialysis patients. METHODS: 161,265 patients in the United States Renal Data System (USRDS) initiated on end-stage renal disease (ESRD) therapy between 1 April 1995 and 30 June 1997 who had data sufficient to calculate BMI were analyzed in an historical cohort study. Cox Regression analysis was used to model the association of BMI and rates of listing for renal transplantation, censored for death and receipt of renal transplant, and adjusted for demographics, comorbidities in the Medical Evidence Form (2728) and in comparison with patient survival. RESULTS: In univariate analysis, only patients with BMI <21.3 kg/m(2) had a statistically significant lower rate of listing compared to patients with BMI 24.5-28.6 kg/m(2) (6.1 vs. 7.5/100 person years). In Cox Regression analysis, patients with BMI <21.3 kg/m(2) had a 18% lower adjusted rate of listing and a 38% lower rate of survival, and patients with BMI >=24.5-28.7 had an 11% higher adjusted rate of listing and no significant difference in adjusted survival compared with patients with BMI>=28.7 kg/m(2). Caucasian females were disproportionately affected by high BMI. CONCLUSIONS: Among ESRD patients, lower BMI was independently associated with reduced adjusted rates of listing. High BMI affected rates of listing disproportionately in caucasian females.

Impact of renal transplantation on survival in end-stage renal disease patients with elevated body mass index.

BACKGROUND: Cadaveric renal transplantation is associated with a survival advantage compared with dialysis patients remaining on the renal transplantation waiting list, but this advantage has not been confirmed in obese end-stage renal disease (ESRD) patients. METHODS: Using data from the USRDS, we studied 7521 patients who presented with ESRD from 1 April 1995 to 29 June 1999 and later enrolled on the renal transplantation waiting list with body mass indices (BMI) >or=30 kg/m(2) at the time of presentation to ESRD, and followed until 6 November 2000. Recipients of preemptive renal transplantation or organs other than kidneys were excluded. Cox non-proportional hazards regression models were used to calculate adjusted, time-dependent hazard ratios (HR) for time to death in a given patient during the study period, controlling for renal transplantation, demographics and comorbidities (Form 2728). RESULTS: The incidence of mortality was 3.3 episodes per 100 patient-years (PY) in cadaveric renal transplantation and 1.9/100 PY in living donor renal transplantation compared with 6.6 episodes/100 PY in all patients on the transplant waiting list. In comparison to maintenance dialysis, both recipients of solitary cadaveric kidneys (HR 0.39, 95% CI 0.33 to 0.47), and recipients of living donor kidneys (HR 0.23, 95% CI 0.16 to 0.34) had statistically significant improved survival. A benefit of cadaveric renal transplantation did not apply to patients with BMI >or=41 kg/m(2) (HR 0.47, 95% CI, 0.17 to 1.25, P = 0.13). CONCLUSIONS: Obese patients on the renal transplant waiting list had a significantly lower risk of mortality after renal transplantation compared with those remaining on dialysis.

Factors associated with improved short term survival in obese end stage renal disease patients.

PURPOSE: In contrast to its role in the general population, obesity, defined as body mass index (BMI) > or = 30 kg/m(2), has been associated with improved survival in patients with end stage renal disease (ESRD). This apparent benefit has not been explained. METHODS: Using the United States Renal Data System (USRDS), we performed an historical cohort study on 151,027 patients initiated on ESRD therapy between January 1, 1995 and June 30, 1997, who never received renal transplants, and who had information sufficient to calculate BMI. We explored the association of various comorbidities present at the time of dialysis initiation (from HCFA Form 2728) with the presence of obesity by logistic regression, and the association of obesity with patient survival, including specific causes of death, by Cox regression adjusting for factors known to be associated with survival in this population. RESULTS: Obese patients had an unadjusted two-year survival of 68% compared with 58% for non obese patients. Obesity was independently associated with a reduced risk of mortality among chronic dialysis patients (adjusted hazard ratio (AHR) 0.75, 95% confidence interval, 0.72-0.78), after controlling for all comorbidities and risk factors. However, there were significantly adverse interactions among whites (AHR 1.22, 1.14-1.30, across all causes of death) and females (AHR 1.12, 1.04-1.20, entirely due to an increased risk of infectious death). CONCLUSIONS: Obesity in patients presenting with ESRD is associated independently with reduced all cause mortality; however, the relationship is complex and is stronger in African Americans. In addition, subgroup analysis suggests that obesity is associated with increased risk of infectious death in females.