title: Determinants of circulating soluble transferrin receptor level in chronic haemodialysis patients.
abstract: BACKGROUND
  The aim of this study was to identify the factors determining the circulating soluble transferrin receptor (sTfR) concentrations in haemodialysis (HD) patients on maintenance recombinant human erythropoietin (rHuEpo) treatment.
  
  
  METHODS
  In a prospective cross-sectional study, 91 chronic HD patients and 18 anaemic controls with normal renal function were recruited. For each subject, blood samples were measured for complete blood count, reticulocyte count, percentage of hypochromic red cells (% HRC), serum ferritin, serum iron, transferrin saturation (TS), serum erythropoietin (sEpo), C-reactive protein (CRP), and sTfR. HD patients received constant rHuEpo doses and basal sEpo was measured > or = 86 h after the last injection. The age, gender, dialysis vintage, and the above-mentioned parameters were used as independent variables and logarithmic sTfR (log(10)sTfR) as a dependent variable in the forward stepwise multiple regression model.
  
  
  RESULTS
  HD patients were similar to controls regarding haematocrit, serum ferritin, TS, and % HRC, but had significantly lower sTfR, sEpo, and reticulocyte index. Univariate analyses showed that the sTfR level strongly correlated with sEpo (r=0.60, P<0.001) and % HRC (r=0.60, P<0.001), and significantly with serum ferritin (r=-0.29, P<0.01), TS (r=-0.27, P<0.05), and dose of rHuEpo administered (r=0.27, P<0.05) in HD patients. sTfR also had a positive correlation with haematocrit (r=0.26, P<0.05), red blood cell (RBC) count (r=0.23, P<0.05), and reticulocyte count (r=0.24, P<0.05), but not with CRP (r=0.16, P>0.05). Multivariate regression analysis disclosed that sEpo, HRC, and serum ferritin were the independent predictors of sTfR level. Overall, the model explained 58.8% of the variability in sTfR (R(2)=0.588, P<0.001).
  
  
  CONCLUSIONS
  Circulating sTfR is a good index of marrow erythropoietic activity in HD patients during rHuEpo treatment. Its level is also independently up-regulated by functional iron deficiency in the process of enhanced erythropoiesis. Our study showed that sTfR levels quantitatively reflect the integrated effects of iron availability, iron reserves, and erythropoietic stimulation.
authors.affiliation: Division of Nephrology, Department of Medicine, Taipei Veterans General Hospital and Faculty of Medicine, National Yang-Ming University School of Medicine, Taipei, Taiwan. dctarng@vghtpe.gov.tw
authors.forename: Der-Cherng
authors.initials: DC
authors.lastname: Tarng
authors.forename: Tung-Po
authors.initials: TP
authors.lastname: Huang
mesh_terms: D015415:Biomarkers / Q000097:blood; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D000068817:Epoetin Alfa; D004920:Erythropoiesis / Q000502:physiology*; D004921:Erythropoietin / Q000627:therapeutic use; D005260:Female; D006397:Hematinics / Q000627:therapeutic use; D006801:Humans; D007501:Iron / Q000378:metabolism; D007676:Kidney Failure, Chronic / Q000097:blood* / Q000188:drug therapy; D008297:Male; D008875:Middle Aged; D011990:Receptors, Transferrin / Q000097:blood*; D011994:Recombinant Proteins; D012044:Regression Analysis; D006435:Renal Dialysis
chemical_list: D015415:Biomarkers; D006397:Hematinics; D011990:Receptors, Transferrin; D011994:Recombinant Proteins; D004921:Erythropoietin; D000068817:Epoetin Alfa; D007501:Iron