Title: Erythropoietin and iron-restricted erythropoiesis
Abstract: Twenty five years ago, Finch summarized knowledge gained primarily from studies of normal individuals, patients with hereditary hemolytic anemias, and patients with hemochromatosis [1Finch C.A. Erythropoiesis, erythropoietin, and iron.Blood. 1982; 60: 1241-1246PubMed Google Scholar]. Under conditions of basal erythropoiesis in normal subjects, plasma iron turnover (as an index of marrow erythropoietic response) is little affected, whether transferrin saturation ranges from very low to very high levels. In contrast, the erythropoietic response in individuals with congenital hemolytic anemia, in whom erythropoiesis is chronically raised up to sixfold over basal levels [2Crosby W.H. The metabolism of hemoglobin and bile pigment in hemolytic disease.Am J Med. 1955; 18: 112-122Abstract Full Text PDF PubMed Scopus (33) Google Scholar], is affected (and limited) by serum iron levels and by transferrin saturation [3Hillman R.S. Henderson P.A. Control of marrow production by the level of iron supply.J Clin Invest. 1969; 48: 454-460Crossref PubMed Scopus (115) Google Scholar]. Patients with hemochromatosis who underwent serial phlebotomy were observed to mount erythropoietic responses of up to eightfold over basal rates, attributed to the maintenance of very high serum iron and transferrin saturation levels in these patients [4Crosby W.H. Treatment of haemochromatosis by energetic phlebotomy. One patient's response to the letting of 55 liters of blood in 11 months.Br J Haematol. 1958; 4: 82-88Crossref PubMed Scopus (42) Google Scholar], whereas normal individuals were shown to have difficulty providing sufficient iron to support rates of erythropoiesis greater than three times basal rates [5Coleman P.H. Stevens A.R. Dodge H.T. Finch C.A. Rate of regeneration after blood loss.AMA Arch Intern Med. 1953; 92: 341-348Crossref PubMed Scopus (67) Google Scholar]. These observations led Finch to identify a "relative iron deficiency" state, also known as "functional iron deficiency," which he defined as circumstances in which increased erythron iron requirements exceed the available supply of iron [6Finch C.A. Perspectives in iron metabolism.N Engl J Med. 1982; 25: 1520-1528Crossref Scopus (309) Google Scholar]. In another clinical setting, patients undergoing autologous blood donation represent a model for perisurgical blood loss and the erythropoietic response. Insights gained over the last 20 years regarding the relationship between erythropoietin, iron, and erythropoiesis, along with implications for clinical management, will be reviewed. Twenty five years ago, Finch summarized knowledge gained primarily from studies of normal individuals, patients with hereditary hemolytic anemias, and patients with hemochromatosis [1Finch C.A. Erythropoiesis, erythropoietin, and iron.Blood. 1982; 60: 1241-1246PubMed Google Scholar]. Under conditions of basal erythropoiesis in normal subjects, plasma iron turnover (as an index of marrow erythropoietic response) is little affected, whether transferrin saturation ranges from very low to very high levels. In contrast, the erythropoietic response in individuals with congenital hemolytic anemia, in whom erythropoiesis is chronically raised up to sixfold over basal levels [2Crosby W.H. The metabolism of hemoglobin and bile pigment in hemolytic disease.Am J Med. 1955; 18: 112-122Abstract Full Text PDF PubMed Scopus (33) Google Scholar], is affected (and limited) by serum iron levels and by transferrin saturation [3Hillman R.S. Henderson P.A. Control of marrow production by the level of iron supply.J Clin Invest. 1969; 48: 454-460Crossref PubMed Scopus (115) Google Scholar]. Patients with hemochromatosis who underwent serial phlebotomy were observed to mount erythropoietic responses of up to eightfold over basal rates, attributed to the maintenance of very high serum iron and transferrin saturation levels in these patients [4Crosby W.H. Treatment of haemochromatosis by energetic phlebotomy. One patient's response to the letting of 55 liters of blood in 11 months.Br J Haematol. 1958; 4: 82-88Crossref PubMed Scopus (42) Google Scholar], whereas normal individuals were shown to have difficulty providing sufficient iron to support rates of erythropoiesis greater than three times basal rates [5Coleman P.H. Stevens A.R. Dodge H.T. Finch C.A. Rate of regeneration after blood loss.AMA Arch Intern Med. 1953; 92: 341-348Crossref PubMed Scopus (67) Google Scholar]. These observations led Finch to identify a "relative iron deficiency" state, also known as "functional iron deficiency," which he defined as circumstances in which increased erythron iron requirements exceed the available supply of iron [6Finch C.A. Perspectives in iron metabolism.N Engl J Med. 1982; 25: 1520-1528Crossref Scopus (309) Google Scholar]. In another clinical setting, patients undergoing autologous blood donation represent a model for perisurgical blood loss and the erythropoietic response. Insights gained over the last 20 years regarding the relationship between erythropoietin, iron, and erythropoiesis, along with implications for clinical management, will be reviewed. Autologous blood donation in patients scheduled for elective surgery results in blood-loss anemia. Patients undergoing autologous blood phlebotomy may donate a unit (450 ± 45 mL) of blood as often as twice weekly, until 72 hours before surgery [8Menitove J. Standards for Blood Banks and Transfusion Services. 19th ed. American Association of Blood Banks, Bethesda, MD1999: 76Google Scholar]. Under routine conditions, patients usually donate once weekly [9Goodnough L.T. Brittenham G. Limitations of the erythropoietic response to serial phlebotomy: implications for autologous blood predeposit programs.J Lab Clin Med. 1990; 115: 28-35PubMed Google Scholar]. Oral iron supplements are routinely prescribed. This iatrogenic blood loss is accompanied by a response in endogenous erythropoietin levels that, while increased significantly over basal levels, remain within the normal range (4–26 mU/mL) [10Kickler T.S. Spivak J.L. Effect of repeated whole blood donations on serum immunoreactive erythropoietin levels in autologous donors.JAMA. 1988; 260: 65-67Crossref PubMed Scopus (173) Google Scholar]. The erythropoietic response that occurs under these conditions is modest [7Goodnough L.T. Skikne B. Brugnara C. Erythropoietin, iron, and erythropoiesis.Blood. 2000; 96: 823-833PubMed Google Scholar, 8Menitove J. Standards for Blood Banks and Transfusion Services. 19th ed. American Association of Blood Banks, Bethesda, MD1999: 76Google Scholar]. A summary of selected prospective, controlled trials [11Kasper S.M. Gerlich W. Buzello W. Preoperative red cell production in patients undergoing weekly autologous blood donation.Transfusion. 1997; 37: 1058-1062Crossref PubMed Scopus (51) Google Scholar, 12Kasper S.M. Lazansky H. Stark C. Klimek M. Laubinger R. Börner Y. Efficacy of oral iron supplementation is not enhanced by additional intravenous iron during autologous blood donation.Transfusion. 1998; 38: 764-770Crossref PubMed Scopus (36) Google Scholar, 13Weisbach V. Skoda P. Rippel R. et al.Oral or intravenous iron as an adjunct to autologous blood donation in elective surgery: a randomized, controlled study.Transfusion. 1999; 39: 465-472Crossref PubMed Scopus (47) Google Scholar, 14Goodnough L.T. Rudnick S. Price T.H. et al.Increased preoperative collection of autologous blood with recombinant human erythropoietin therapy.N Engl J Med. 1989; 321: 1163-1168Crossref PubMed Scopus (424) Google Scholar, 15Goodnough L.T. Price T.H. Rudnick S. Soegiarso R.W. Preoperative red blood cell production in patients undergoing aggressive autologous blood phlebotomy with and without erythropoietin therapy.Transfusion. 1992; 32: 441-445Crossref PubMed Scopus (129) Google Scholar, 16Goodnough L.T. Price T.H. Friedman K.D. et al.A phase III trial of recombinant human erythropoietin therapy in non-anemic orthopedic patients subjected to aggressive autologous blood phlebotomy: dose, response, toxicity, efficacy.Transfusion. 1994; 34: 66-71Crossref PubMed Scopus (115) Google Scholar] of patients undergoing phlebotomy is presented in Table 1. Calculated estimates of red blood cell (RBC) volume expansion (erythropoiesis in excess of basal rates) were determined [17Brecher M.A. Monk T.G. Goodnough L.T. A standardized method for calculating blood loss.Transfusion. 1997; 37: 1070-1074Crossref PubMed Scopus (208) Google Scholar]. Two-hundred and twenty to 351 mL (11–19% RBC expansion [11Kasper S.M. Gerlich W. Buzello W. Preoperative red cell production in patients undergoing weekly autologous blood donation.Transfusion. 1997; 37: 1058-1062Crossref PubMed Scopus (51) Google Scholar, 12Kasper S.M. Lazansky H. Stark C. Klimek M. Laubinger R. Börner Y. Efficacy of oral iron supplementation is not enhanced by additional intravenous iron during autologous blood donation.Transfusion. 1998; 38: 764-770Crossref PubMed Scopus (36) Google Scholar] or the equivalent of 1–1.75 blood units [18Goodnough L.T. Bravo J. Hsueh Y. Keating L. Brittenham G.M. Red blood cell volume in autologous and homologous blood units. Implications for risk benefit assessment for autologous blood "crossover" and directed blood transfusion.Transfusion. 1989; 29: 821-822Crossref PubMed Scopus (74) Google Scholar]) are produced in excess of basal erythropoiesis, defining the efficacy of this blood conservation practice.Table 1Endogenous erythropoietin-mediated erythropoiesisPatients (n)Baseline RBC (mL)Requested/donated unitsRBC donated (mL)RBC produced (mL)RBC (mL) expansion (%)Iron therapyRef.Standard phlebotomy10818843/2.752235119PO11Kasper S.M. Gerlich W. Buzello W. Preoperative red cell production in patients undergoing weekly autologous blood donation.Transfusion. 1997; 37: 1058-1062Crossref PubMed Scopus (51) Google Scholar2219363/2.859022011None12Kasper S.M. Lazansky H. Stark C. Klimek M. Laubinger R. Börner Y. Efficacy of oral iron supplementation is not enhanced by additional intravenous iron during autologous blood donation.Transfusion. 1998; 38: 764-770Crossref PubMed Scopus (36) Google Scholar4519913/2.962133117PO12Kasper S.M. Lazansky H. Stark C. Klimek M. Laubinger R. Börner Y. Efficacy of oral iron supplementation is not enhanced by additional intravenous iron during autologous blood donation.Transfusion. 1998; 38: 764-770Crossref PubMed Scopus (36) Google Scholar4119183/2.960331516PO + IV12Kasper S.M. Lazansky H. Stark C. Klimek M. Laubinger R. Börner Y. Efficacy of oral iron supplementation is not enhanced by additional intravenous iron during autologous blood donation.Transfusion. 1998; 38: 764-770Crossref PubMed Scopus (36) Google ScholarAggressive phlebotomy302075≥3/3.054039719None13Weisbach V. Skoda P. Rippel R. et al.Oral or intravenous iron as an adjunct to autologous blood donation in elective surgery: a randomized, controlled study.Transfusion. 1999; 39: 465-472Crossref PubMed Scopus (47) Google Scholar302024≥3/3.155847323PO13Weisbach V. Skoda P. Rippel R. et al.Oral or intravenous iron as an adjunct to autologous blood donation in elective surgery: a randomized, controlled study.Transfusion. 1999; 39: 465-472Crossref PubMed Scopus (47) Google Scholar302057≥3/2.952243621IV13Weisbach V. Skoda P. Rippel R. et al.Oral or intravenous iron as an adjunct to autologous blood donation in elective surgery: a randomized, controlled study.Transfusion. 1999; 39: 465-472Crossref PubMed Scopus (47) Google Scholar2421576/4.168356826PO14Goodnough L.T. Rudnick S. Price T.H. et al.Increased preoperative collection of autologous blood with recombinant human erythropoietin therapy.N Engl J Med. 1989; 321: 1163-1168Crossref PubMed Scopus (424) Google Scholar, 15Goodnough L.T. Price T.H. Rudnick S. Soegiarso R.W. Preoperative red blood cell production in patients undergoing aggressive autologous blood phlebotomy with and without erythropoietin therapy.Transfusion. 1992; 32: 441-445Crossref PubMed Scopus (129) Google Scholar2322576/4.675744019PO16Goodnough L.T. Price T.H. Friedman K.D. et al.A phase III trial of recombinant human erythropoietin therapy in non-anemic orthopedic patients subjected to aggressive autologous blood phlebotomy: dose, response, toxicity, efficacy.Transfusion. 1994; 34: 66-71Crossref PubMed Scopus (115) Google ScholarData expressed as means. Modified from Goodnough et al. 7Goodnough L.T. Skikne B. Brugnara C. Erythropoietin, iron, and erythropoiesis.Blood. 2000; 96: 823-833PubMed Google Scholar.IV = intravenous; PO = oral; RBC = red blood cells. Open table in a new tab Data expressed as means. Modified from Goodnough et al. 7Goodnough L.T. Skikne B. Brugnara C. Erythropoietin, iron, and erythropoiesis.Blood. 2000; 96: 823-833PubMed Google Scholar. IV = intravenous; PO = oral; RBC = red blood cells. For patients subjected to more aggressive (up to 2 U weekly) phlebotomy, the endogenous erythropoietin response is more substantial [13Weisbach V. Skoda P. Rippel R. et al.Oral or intravenous iron as an adjunct to autologous blood donation in elective surgery: a randomized, controlled study.Transfusion. 1999; 39: 465-472Crossref PubMed Scopus (47) Google Scholar, 14Goodnough L.T. Rudnick S. Price T.H. et al.Increased preoperative collection of autologous blood with recombinant human erythropoietin therapy.N Engl J Med. 1989; 321: 1163-1168Crossref PubMed Scopus (424) Google Scholar, 15Goodnough L.T. Price T.H. Rudnick S. Soegiarso R.W. Preoperative red blood cell production in patients undergoing aggressive autologous blood phlebotomy with and without erythropoietin therapy.Transfusion. 1992; 32: 441-445Crossref PubMed Scopus (129) Google Scholar, 16Goodnough L.T. Price T.H. Friedman K.D. et al.A phase III trial of recombinant human erythropoietin therapy in non-anemic orthopedic patients subjected to aggressive autologous blood phlebotomy: dose, response, toxicity, efficacy.Transfusion. 1994; 34: 66-71Crossref PubMed Scopus (115) Google Scholar]. In one clinical trial (14), a linear-logarithmic relationship was demonstrated between change in hemoglobin level and erythropoietin response [19Goodnough L.T. Price T.H. Parvin C.A. et al.Erythropoietin response to anaemia is not altered by surgery or recombinant human EPO therapy.Br J Haematol. 1994; 87: 695-699Crossref PubMed Scopus (34) Google Scholar], predicted previously by phlebotomy experiments in normal subjects [20Adamson J.W. The erythropoietin/hematocrit relationship in normal and polycythemic man: implications of marrow regulation.Blood. 1968; 32: 597-609PubMed Google Scholar]. Erythropoietin-mediated erythropoiesis in this setting is 397 to 568 mL (19–26% RBC expansion [13Weisbach V. Skoda P. Rippel R. et al.Oral or intravenous iron as an adjunct to autologous blood donation in elective surgery: a randomized, controlled study.Transfusion. 1999; 39: 465-472Crossref PubMed Scopus (47) Google Scholar, 14Goodnough L.T. Rudnick S. Price T.H. et al.Increased preoperative collection of autologous blood with recombinant human erythropoietin therapy.N Engl J Med. 1989; 321: 1163-1168Crossref PubMed Scopus (424) Google Scholar, 15Goodnough L.T. Price T.H. Rudnick S. Soegiarso R.W. Preoperative red blood cell production in patients undergoing aggressive autologous blood phlebotomy with and without erythropoietin therapy.Transfusion. 1992; 32: 441-445Crossref PubMed Scopus (129) Google Scholar, 16Goodnough L.T. Price T.H. Friedman K.D. et al.A phase III trial of recombinant human erythropoietin therapy in non-anemic orthopedic patients subjected to aggressive autologous blood phlebotomy: dose, response, toxicity, efficacy.Transfusion. 1994; 34: 66-71Crossref PubMed Scopus (115) Google Scholar], or the equivalent of 2–3 blood units [18Goodnough L.T. Bravo J. Hsueh Y. Keating L. Brittenham G.M. Red blood cell volume in autologous and homologous blood units. Implications for risk benefit assessment for autologous blood "crossover" and directed blood transfusion.Transfusion. 1989; 29: 821-822Crossref PubMed Scopus (74) Google Scholar]). Clinical trials have demonstrated a dose–response relationship between recombinant human erythropoietin (EPO) therapy and red blood cell expansion [16Goodnough L.T. Price T.H. Friedman K.D. et al.A phase III trial of recombinant human erythropoietin therapy in non-anemic orthopedic patients subjected to aggressive autologous blood phlebotomy: dose, response, toxicity, efficacy.Transfusion. 1994; 34: 66-71Crossref PubMed Scopus (115) Google Scholar]. A study of EPO therapy in autologous blood donors found that 400 U/kg administered over a 2-week interval resulted in clinically significant erythropoiesis [21Sans T. Bofill C. Joven J. et al.Effectiveness of very low doses of subcutaneous recombinant human erythropoietin in facilitating autologous blood donation before orthopedic surgery.Transfusion. 1996; 36: 822-826Crossref PubMed Scopus (38) Google Scholar]. Table 2 details red cell volume expansion in 134 patients treated with EPO therapy during aggressive blood phlebotomy [14Goodnough L.T. Rudnick S. Price T.H. et al.Increased preoperative collection of autologous blood with recombinant human erythropoietin therapy.N Engl J Med. 1989; 321: 1163-1168Crossref PubMed Scopus (424) Google Scholar, 15Goodnough L.T. Price T.H. Rudnick S. Soegiarso R.W. Preoperative red blood cell production in patients undergoing aggressive autologous blood phlebotomy with and without erythropoietin therapy.Transfusion. 1992; 32: 441-445Crossref PubMed Scopus (129) Google Scholar, 16Goodnough L.T. Price T.H. Friedman K.D. et al.A phase III trial of recombinant human erythropoietin therapy in non-anemic orthopedic patients subjected to aggressive autologous blood phlebotomy: dose, response, toxicity, efficacy.Transfusion. 1994; 34: 66-71Crossref PubMed Scopus (115) Google Scholar, 22Mercuriali F. Inghilleri Biffi E. Colotti M.T. Vinci A. Oriani G. Epoietin alfa in low hematocrit patients to facilitate autologous blood donation in total hip replacement: a randomized, double-blind, placebo-controlled, dose-ranging study.Acta Haematol. 1998; 100: 69-76Crossref PubMed Scopus (20) Google Scholar, 23Brugnara C. Chambers L.A. Malynn E. Goldberg M.A. Kruskall M.S. Red blood cell regeneration induced by subcutaneous recombinant erythropoietin: iron-deficient erythropoiesis in iron-replete subjects.Blood. 1993; 81: 956-964PubMed Google Scholar], ranging from 358 to 1764 mL (28–79% RBC expansion) over 25 to 35 days, or the equivalent of 2 to 9 blood units [18Goodnough L.T. Bravo J. Hsueh Y. Keating L. Brittenham G.M. Red blood cell volume in autologous and homologous blood units. Implications for risk benefit assessment for autologous blood "crossover" and directed blood transfusion.Transfusion. 1989; 29: 821-822Crossref PubMed Scopus (74) Google Scholar]. The range in response (erythropoiesis) to dose (erythropoietin) is not related to patient gender or age [24Goodnough L.T. Verbrugge D. Marcus R.E. Goldberg V. The effect of patient size and dose of recombinant human erythropoietin therapy on red blood cell expansion.J Am Coll Surg. 1994; 179: 171-176PubMed Google Scholar, 25Goodnough L.T. Price T.H. Parvin C.A. The endogenous erythropoietin response and the erythropoietic response to blood loss anemia: the effects of age and gender.J Lab Clin Med. 1995; 126: 57-64PubMed Google Scholar], suggesting that iron-restricted erythropoiesis may account for the variability in erythropoietic response to EPO.Table 2Erythropoiesis during blood loss and erythropoietin therapyPatients (n/gender)Baseline RBC (mL)Total EPO dose (U/kg)Units donatedRBC donated (mL)RBC produced (mL)RBC (mL) expansion (%)Iron therapyRef.10/F1285900 SQ3.443535828IV22Mercuriali F. Inghilleri Biffi E. Colotti M.T. Vinci A. Oriani G. Epoietin alfa in low hematocrit patients to facilitate autologous blood donation in total hip replacement: a randomized, double-blind, placebo-controlled, dose-ranging study.Acta Haematol. 1998; 100: 69-76Crossref PubMed Scopus (20) Google Scholar241949900 IV5.286462132PO16Goodnough L.T. Price T.H. Friedman K.D. et al.A phase III trial of recombinant human erythropoietin therapy in non-anemic orthopedic patients subjected to aggressive autologous blood phlebotomy: dose, response, toxicity, efficacy.Transfusion. 1994; 34: 66-71Crossref PubMed Scopus (115) Google Scholar10/F12931800 SQ4.352647437IV22Mercuriali F. Inghilleri Biffi E. Colotti M.T. Vinci A. Oriani G. Epoietin alfa in low hematocrit patients to facilitate autologous blood donation in total hip replacement: a randomized, double-blind, placebo-controlled, dose-ranging study.Acta Haematol. 1998; 100: 69-76Crossref PubMed Scopus (20) Google Scholar2620321800 IV5.591764432PO16Goodnough L.T. Price T.H. Friedman K.D. et al.A phase III trial of recombinant human erythropoietin therapy in non-anemic orthopedic patients subjected to aggressive autologous blood phlebotomy: dose, response, toxicity, efficacy.Transfusion. 1994; 34: 66-71Crossref PubMed Scopus (115) Google Scholar11/F17963600 IV4.980970139PO14Goodnough L.T. Rudnick S. Price T.H. et al.Increased preoperative collection of autologous blood with recombinant human erythropoietin therapy.N Engl J Med. 1989; 321: 1163-1168Crossref PubMed Scopus (424) Google Scholar, 15Goodnough L.T. Price T.H. Rudnick S. Soegiarso R.W. Preoperative red blood cell production in patients undergoing aggressive autologous blood phlebotomy with and without erythropoietin therapy.Transfusion. 1992; 32: 441-445Crossref PubMed Scopus (129) Google Scholar12/M22963600 IV5.91097110248PO14Goodnough L.T. Rudnick S. Price T.H. et al.Increased preoperative collection of autologous blood with recombinant human erythropoietin therapy.N Engl J Med. 1989; 321: 1163-1168Crossref PubMed Scopus (424) Google Scholar, 15Goodnough L.T. Price T.H. Rudnick S. Soegiarso R.W. Preoperative red blood cell production in patients undergoing aggressive autologous blood phlebotomy with and without erythropoietin therapy.Transfusion. 1992; 32: 441-445Crossref PubMed Scopus (129) Google Scholar2320493600 IV5.497091145PO14Goodnough L.T. Rudnick S. Price T.H. et al.Increased preoperative collection of autologous blood with recombinant human erythropoietin therapy.N Engl J Med. 1989; 321: 1163-1168Crossref PubMed Scopus (424) Google Scholar, 15Goodnough L.T. Price T.H. Rudnick S. Soegiarso R.W. Preoperative red blood cell production in patients undergoing aggressive autologous blood phlebotomy with and without erythropoietin therapy.Transfusion. 1992; 32: 441-445Crossref PubMed Scopus (129) Google Scholar1820193600 IV5.697285642PO16Goodnough L.T. Price T.H. Friedman K.D. et al.A phase III trial of recombinant human erythropoietin therapy in non-anemic orthopedic patients subjected to aggressive autologous blood phlebotomy: dose, response, toxicity, efficacy.Transfusion. 1994; 34: 66-71Crossref PubMed Scopus (115) Google Scholar1/M22414200 IV81600176479Hemachromatosis23Brugnara C. Chambers L.A. Malynn E. Goldberg M.A. Kruskall M.S. Red blood cell regeneration induced by subcutaneous recombinant erythropoietin: iron-deficient erythropoiesis in iron-replete subjects.Blood. 1993; 81: 956-964PubMed Google ScholarData expressed as means. Modified from Goodnough et al. 7Goodnough L.T. Skikne B. Brugnara C. Erythropoietin, iron, and erythropoiesis.Blood. 2000; 96: 823-833PubMed Google Scholar.EPO = erythropoietin; F = female; IV = intravenous; M = male; PO = oral; RBC = red blood cells; SQ = subcutaneous. Open table in a new tab Data expressed as means. Modified from Goodnough et al. 7Goodnough L.T. Skikne B. Brugnara C. Erythropoietin, iron, and erythropoiesis.Blood. 2000; 96: 823-833PubMed Google Scholar. EPO = erythropoietin; F = female; IV = intravenous; M = male; PO = oral; RBC = red blood cells; SQ = subcutaneous. Erythropoiesis in response to aggressive autologous phlebotomy via endogenous erythropoietin has been estimated to increase by up to threefold [16Goodnough L.T. Price T.H. Friedman K.D. et al.A phase III trial of recombinant human erythropoietin therapy in non-anemic orthopedic patients subjected to aggressive autologous blood phlebotomy: dose, response, toxicity, efficacy.Transfusion. 1994; 34: 66-71Crossref PubMed Scopus (115) Google Scholar, 26Goodnough L.T. Marcus R.E. Erythropoiesis in iron-depleted and iron-replete patients stimulated with erythropoietin: the relevance of storage iron.Vox Sang. 1998; 75: 128-133Crossref PubMed Google Scholar]. No apparent relationship exists between basal iron stores and this magnitude of erythropoiesis, suggesting that under conditions of moderate erythropoiesis, serum iron, and transferrin saturation for erythron requirements are adequately maintained by storage iron [13Weisbach V. Skoda P. Rippel R. et al.Oral or intravenous iron as an adjunct to autologous blood donation in elective surgery: a randomized, controlled study.Transfusion. 1999; 39: 465-472Crossref PubMed Scopus (47) Google Scholar, 14Goodnough L.T. Rudnick S. Price T.H. et al.Increased preoperative collection of autologous blood with recombinant human erythropoietin therapy.N Engl J Med. 1989; 321: 1163-1168Crossref PubMed Scopus (424) Google Scholar, 15Goodnough L.T. Price T.H. Rudnick S. Soegiarso R.W. Preoperative red blood cell production in patients undergoing aggressive autologous blood phlebotomy with and without erythropoietin therapy.Transfusion. 1992; 32: 441-445Crossref PubMed Scopus (129) Google Scholar, 16Goodnough L.T. Price T.H. Friedman K.D. et al.A phase III trial of recombinant human erythropoietin therapy in non-anemic orthopedic patients subjected to aggressive autologous blood phlebotomy: dose, response, toxicity, efficacy.Transfusion. 1994; 34: 66-71Crossref PubMed Scopus (115) Google Scholar]. Little or no benefit to oral iron supplementation was found in two studies [13Weisbach V. Skoda P. Rippel R. et al.Oral or intravenous iron as an adjunct to autologous blood donation in elective surgery: a randomized, controlled study.Transfusion. 1999; 39: 465-472Crossref PubMed Scopus (47) Google Scholar, 27Biesma D.H. Kraaijenhagen R.J. Poortman J. Marx J.J.M. Van De Wiel A. The effect of oral iron supplementation on erythropoiesis in autologous blood donors.Transfusion. 1992; 32: 162-165Crossref PubMed Scopus (62) Google Scholar], whereas a third study [12Kasper S.M. Lazansky H. Stark C. Klimek M. Laubinger R. Börner Y. Efficacy of oral iron supplementation is not enhanced by additional intravenous iron during autologous blood donation.Transfusion. 1998; 38: 764-770Crossref PubMed Scopus (36) Google Scholar] found some benefit (Table 1). Intravenous iron supplementation was not found to be of value in enhancing erythropoiesis under these conditions [12Kasper S.M. Lazansky H. Stark C. Klimek M. Laubinger R. Börner Y. Efficacy of oral iron supplementation is not enhanced by additional intravenous iron during autologous blood donation.Transfusion. 1998; 38: 764-770Crossref PubMed Scopus (36) Google Scholar, 13Weisbach V. Skoda P. Rippel R. et al.Oral or intravenous iron as an adjunct to autologous blood donation in elective surgery: a randomized, controlled study.Transfusion. 1999; 39: 465-472Crossref PubMed Scopus (47) Google Scholar]. With enhanced erythropoiesis during EPO therapy, iron-restricted erythropoiesis occurs even in patients with measurable storage iron. Despite an eightfold increase in gastrointestinal iron absorption [28Skikne B.S. Cook J.D. Effect of enhanced erythropoiesis on iron absorption.J Lab Clin Med. 1992; 120: 746-751PubMed Google Scholar], serum ferritin and transferrin saturation levels decline up to 50% with EPO therapy [29Heiss M.M. Tarabichi A. Delanoff C. et al.Perisurgical erythropoietin application in anemic patients with colorectal cancer: a double-blind randomized study.Surgery. 1996; 119: 523-527Abstract Full Text PDF PubMed Scopus (64) Google Scholar]. A fourfold increase in erythropoietic activity is accompanied by declining reticulocyte counts and the appearance of hypochromic red cells by the second week of EPO therapy [23Brugnara C. Chambers L.A. Malynn E. Goldberg M.A. Kruskall M.S. Red blood cell regeneration induced by subcutaneous recombinant erythropoietin: iron-deficient erythropoiesis in iron-replete subjects.Blood. 1993; 81: 956-964PubMed Google Scholar, 30Biesma D.H. Van De Wiel A. Beguin Y. Kraaijenhagen R.J. Marx J.J.M. Erythropoietic activity and iron metabolism in autologous blood donors during recombinant human erythropoietin therapy.Eur J Clin Invest. 1994; 24: 426-432Crossref PubMed Scopus (37) Google Scholar]. In a study of escalating (fourfold) increase in EPO dose administered to patients undergoing aggressive phlebotomy, the marrow erythropoietic index increased from 2.9-fold (with endogenous erythropoietin stimulation) to 3.6-fold over basal rates of erythropoiesis, representing only a 58% increase in erythropoiesis (Fig. 1). The superior erythropoietic response in a patient with hemochromatosis further suggests iron-restricted erythropoiesis in patients treated with EPO (Table 2, [23Brugnara C. Chambers L.A. Malynn E. Goldberg M.A. Kruskall M.S. Red blood cell regeneration induced by subcutaneous recombinant erythropoietin: iron-deficient erythropoiesis in iron-replete subjects.Blood. 1993; 81: 956-964PubMed Google Scholar]). The success of EPO therapy in correcting the anemia of chronic renal failure has led to substantial clinical experience in iron therapy and erythropoiesis in this setting [31Eschbach J. Egrie J. Downing M. Browne J.K. Adamson J.W. Correction of anemia of end-stage renal disease with recombinant human erythropoietin.N Engl J Med. 1987; 316: 73-78Crossref PubMed Scopus (1796) Google Scholar, 32Fishbane S. Frei G.L. Maesaka J. Reduction in recombinant human erythropoietin doses by the use of chronic intravenous iron supplement