Duration of Anemia Predicts Death in Dialysis Patients


MINNEAPOLIS, Dec. 6 -- A persistently low hemoglobin level is more closely associated with mortality in dialysis patients than variability in hemoglobin, researchers here said.
Action Points --->
Explain that the study found that persistently low hemoglobin values were more predictive of death in dialysis patients than was simple variability in hemoglobin levels.
Explain that physicians cannot fully control hemoglobin levels.
Point out that as an observational study, this study cannot prove causality but only demonstrate the associations.
Patients with hemoglobin levels consistently below 11 g/dL over a six-month period had a hazard ratio of 2.18 (95% CI: 1.93 to 2.45) for death in the following six months, relative to those with consistently intermediate hemoglobin values, David T. Gilbertson, Ph.D., of the Minneapolis Medical Research Foundation, and colleagues reported in the January 2008 issue of the Clinical Journal of the American Society of Nephrology.
"This study suggests that patients who experienced the fewest number of months with hemoglobin levels below the 11 to 12.5 g/dL range experienced the lowest mortality," the researchers said.
Earlier research had shown that hemoglobin variability was associated with comorbidities and hospitalization, they noted, but, said Dr. Gilbertson, "our results suggest that fluctuations in hemoglobin levels probably do not add much to the mortality risk for patients with dialysis-related anemia."
To reach that conclusion, they analyzed Medicare data, including monthly hemoglobin measurements, on 159,720 hemodialysis patients who survived the first six months of 2004 and who were taking erythropoietin (EPO) every month.
Hemoglobin values of less than 11 g/dL, from 11 to 12.5 g/dL, and more than 12.5 g/dL were defined as low, intermediate, and high, respectively. Six variability groups were identified: low-low, intermediate-intermediate, high-high, low-intermediate, intermediate-high, and low-high, based on the lowest and highest values seen in the six-month period.
The hazard ratio for death in the low-high group, reflecting the greatest variability, was 1.19 (95% CI: 1.10 to 1.28) relative to patients with consistently intermediate hemoglobin measurements.
Hemoglobin variability was common, the researchers found, with 40.2% in the low-high category, 31.7% in the intermediate-high group, and 18.3% in low-intermediate.
Some earlier research had found adverse effects of high hemoglobin levels in dialysis patients, but the Minneapolis group found a hazard ratio of death in the high-high group of 1.06 (95% CI: 0.93 to 1.21).
Patients in the consistently low category had the highest risk of death (HR: 2.18, 95% CI: 1.93 to 2.45). The longer the amount of time with a hemoglobin level <11 g/dL, the greater the risk of death; additionally, the timing of the low hemoglobin value within the six-month period was strongly associated with an increased risk of death.
The researchers said they did not attempt to identify causes for the hemoglobin variation, but indicated that some may be related to EPO and iron dosing. The rest, they said, may be the result of hospitalizations, infections, and other conditions and factors beyond the control of the health care system.
"These events would themselves be associated with increased risk of future mortality, and thus such nonactionable variability may be simply a marker for patient illness," they said.
When the group added EPO dosing as a variable in their analysis, it reduced the relative risks associated with anemia. "However, the general patterns were still apparent," they said.
The authors pointed out that, as an observational study, this study cannot prove causality but only demonstrates the associations.
The study was funded by Amgen.
Dr. Gilbertson and several co-authors reported receiving consulting fees from Amgen. One co-author was an Amgen employee.
Primary source: Clinical Journal of the American Society of NephrologySource reference:Gilbertson D, "Hemoglobin level variability: associations with mortality" Clin J Am So Nephrol 2007; DOI: 10.2215/CJN.01610407.