title: Erythropoietin, iron depletion, and relative thrombocytosis: a possible explanation for hemoglobin-survival paradox in hemodialysis.
abstract: BACKGROUND
  High doses of human recombinant erythropoietin (rHuEPO) to achieve hemoglobin levels greater than 13 g/dL in patients with chronic kidney disease appear to be associated with increased mortality.
  
  
  METHODS
  We conducted logistic regression and survival analyses in a retrospective cohort of long-term hemodialysis patients to examine the hypothesis that the induced iron depletion with resultant relative thrombocytosis may be a possible contributor to the link between the high rHuEPO dose-associated hemoglobin level of 13 g/dL or greater and mortality.
  
  
  METHODS
  The national database of a large dialysis organization (DaVita) with 40,787 long-term hemodialysis patients during July to December 2001 and their survival up to July 2004 were examined.
  
  
  METHODS
  Hemoglobin level, platelet count, and administered rHuEPO dose during each calendar quarter.
  
  
  METHODS
  Case-mix-adjusted 3-year all-cause mortality and measures of iron stores, including serum ferritin and iron saturation ratio.
  
  
  RESULTS
  Higher platelet count was associated with lower iron stores and greater prescribed rHuEPO dose. Compared with a hemoglobin level of 12 to 13 g/dL, a hemoglobin level of 13 g/dL or greater was associated with increased mortality in the presence of relative thrombocytosis, ie, platelet count of 300,000/microL or greater (case-mix-adjusted death-rate ratio, 1.21; 95% confidence limits, 1.02 to 1.44; P = 0.03) as opposed to the absence of relative thrombocytosis (death-rate ratio, 1.04; 95% confidence limits, 0.98 to 1.08; P = 0.1). A prescribed rHuEPO dose greater than 20,000 U/wk was associated with a greater likelihood of iron depletion (iron saturation ratio < 20%) and relative thrombocytosis (case-mix-adjusted odds ratio, 2.53; 95% confidence limits, 2.37 to 2.69; and 1.36; 95% confidence limits, 1.30 to 1.42, respectively; P < 0.001) and increased mortality during 3 years (death-rate ratio, 1.59; 95% confidence limits, 1.54 to 1.65; P < 0.001).
  
  
  CONCLUSIONS
  Our results may incorporate uncontrolled confounding. Achieved hemoglobin level may have different mortality predictability than targeted hemoglobin level.
  
  
  CONCLUSIONS
  Iron depletion and associated relative thrombocytosis might contribute to increased mortality when administering high rHuEPO doses to achieve hemoglobin levels of 13 g/dL or greater in long-term hemodialysis patients. Randomized trials are needed to test these observational associations.
authors.affiliation: Harold Simmons Center for Kidney Disease Research and Epidemiology, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA 90509-2910, USA.
authors.forename: Elani
authors.initials: E
authors.lastname: Streja
authors.forename: Csaba P
authors.initials: CP
authors.lastname: Kovesdy
authors.forename: Sander
authors.initials: S
authors.lastname: Greenland
authors.forename: Joel D
authors.initials: JD
authors.lastname: Kopple
authors.forename: Charles J
authors.initials: CJ
authors.lastname: McAllister
authors.forename: Allen R
authors.initials: AR
authors.lastname: Nissenson
authors.forename: Kamyar
authors.initials: K
authors.lastname: Kalantar-Zadeh