Background: The link between dialysis "vintage" (length of time on dialysis in months to years) and survival has been difficult to define, largely because of selection effects. End-stage renal disease (ESRD) is thought to be a wasting illness, but there are no published reports describing the associations between vintage and body composition in hemodialysis patients.
Methods: We explored the relationships among vintage, nutritional status, and survival in a 3009 patient cohort of prevalent hemodialysis patients. Body weight, total body water, body cell mass, and phase angle by bioelectrical impedance analysis were the body composition parameters of interest. We examined vintage as an explanatory variable in multiple linear regression analyses (adjusted for age, gender, race, and diabetes) using body composition parameters and biochemical indicators of nutritional status as dependent variables. Proportional hazards regression was used to evaluate the association of vintage and survival with and without adjustment for case mix and laboratory variables.
Results: Dialysis vintage was 3.8 +/- 3.7 (median 2.6) years. Body composition parameters tended to be lower after dialysis year 2. Linear estimates per year of vintage beyond year 2 include -0.66 kg body wt (P < 0.0001), -0.17 kg total body water (P = 0.0003), -0.14 kg body cell mass (P < 0.0001), and -0.07 degrees phase angle (P < 0.0001). In unadjusted analyses, vintage was not associated with survival, either as a linear or higher order term. The adjustment for case mix yielded a vintage term associated with an increased relative risk (RR) of death (RR 1.04 (95% CI, 1.01 to 1.07 per year). A further adjustment for laboratory data yielded a RR of 1.06 (95% CI, 1.03 to 1.09 per year).
Conclusion: Dialysis vintage is related to nutritional status in hemodialysis patients, with vintage of more than years associated with a significant decline in all measured nutritional parameters. Cross-sectional analyses probably underestimate these effects. A year accrued on dialysis is associated with a 6% increase in the risk of death, all else equal. Longitudinal assessments of nutritional status, including body composition, are required to better understand the natural history of wasting with ESRD and its implications for long-term survival.