Anemia and mortality in hemodialysis patients: accounting for morbidity and treatment variables updated over time.

BACKGROUND: The objective of this study was to gain insight into the associations of anemia with mortality among maintenance hemodialysis (HD) patients and patient subgroups by an analysis that more comprehensively represents hemoglobin (Hb) level, morbidity, and treatment characteristics over time than was possible in prior observational studies.
METHODS: A cohort study was conducted among 5517 subjects in the American arm of the Dialysis Outcomes and Practice Patterns Study Phase I. We used proportional hazard analysis to model all-cause mortality as a function of Hb level measured 1, 3, and 6 months previously. Forty-five potentially confounding patient-level characteristics were considered, including demographics, comorbidities, and time-updated levels of erythropoietin and parenteral iron dosing, medical events, and laboratory and dialysis measures.
RESULTS: Compared to Hb 11 to <12 g/dL, subjects with Hb <11 g/dL had increased mortality [adjusted hazard ratios (95% confidence interval) in the 3-month-lagged model = 1.74 (1.24 to 2.43) for <9 g/dL, 1.25 (0.96 to 1.63) for 9 to <10 g/dL, and 1.22 (0.99 to 1.49) for 10 to <11 g/dL categories]. Mortality rates for subjects with Hb 12 to <13 g/dL and > or = 13 g/dL did not differ significantly from those with Hb 11 to <12 g/dL. The relationships between Hb and mortality varied modestly with changes in the time interval between Hb measurement and the time at risk for mortality, but did not vary according to ESRD vintage or health status indicators.
CONCLUSION: Our findings confirm the associations of Hb levels > or =11 g/dL with longer survival among maintenance HD patients, but show no additional survival advantage for patients with Hb levels > or =12 g/dL. Further investigation of the relationships among anemia, treatment of anemia, and survival is warranted.