We evaluated the quantitative value of a simple model of erythropoiesis, based on the basic assumptions that the red blood cell (RBC) mass determines erythropoietin (Epo) production, which in turn stimulates erythropoietic activity. The RBC mass was quantitated by direct isotopic measurement (RCM), Epo production by serum Epo levels, and erythropoiesis by the ferrokinetic measurement of the erythron transferrin uptake (ETU), the serum transferrin receptor (TfR) level, and the reticulocyte (retic) index, and was completed by an evaluation of overall marrow erythron cellularity. We studied a total of 195 subjects, including 31 normal individuals, 38 patients with polycythemia, and 126 patients with various forms of anemia. Instead of only quantitating Epo and erythropoiesis in absolute terms, we also evaluated them in relation to the degree of anemia or polycythemia, and expressed the results as a ratio of observed values to values predicted from the regression equations between hematocrit (Hct) on the one hand, and Epo, TfR, and ETU on the other, obtained in a carefully selected subpopulation. The slope of the regression of TfR (as well as ETU) versus Hct was very similar to the slope of the regression of Epo versus Hct. Average EPO and TfR (as well as ETU) values predicted from the regression equations were quite comparable to observed values in most groups of subjects, with exceptions predictable from knowledge of the pathophysiology of these hematologic disorders. We identified four major patterns of erythropoiesis, ie, normal, hyperdestruction (with variants of hemolysis or ineffective erythropoiesis), intrinsic marrow hypoproliferation, and defective Epo production. Dissecting out groups of patients showed much greater heterogeneity than when patients were analyzed by group. This was particularly true in the case of a hypoproliferative component being combined with hyperdestruction, giving what we called a “mixed disorder of erythropoiesis.” We conclude that the pathophysiology of anemia can be assessed by a simple measurement of Hct, retic index, Epo, and TfR levels, with Epo and TfR being more informative when expressed in relation to the degree of anemia. The model is particularly useful for detecting the presence of multiple mechanisms of anemia in the same patient. However, it has limitations inherent to the relative invalidity of TfR in iron deficiency, the imprecision of a retic count, and the difficulty in distinguishing hemolysis from ineffective erythropoiesis in some patients and in recognizing a component of hyperdestruction in hypoproliferative anemia.

Iron transport in the reticuloendothelial (RE) system plays a central role in iron metabolism, but its regulation has not been characterized physiologically in vivo in humans. In particular, why serum iron is elevated and RE cells are much less iron-loaded than parenchymal cells in idiopathic hemochromatosis is not known. The processing of erythrocyte iron by the RE system was studied after intravenous (IV) injection of 59Fe heat-damaged RBCs (HDRBCs) and 55Fe transferrin in normal subjects and in patients with iron deficiency, idiopathic hemochromatosis, inflammation, marrow aplasia, or hyperplastic erythropoiesis. Early release of 59Fe by the RE system was calculated from the plasma iron turnover and the 59Fe plasma reappearance curve. Late release was calculated from the ratio of 59Fe/55Fe RBC utilization in 2 weeks. The partitioning of iron between the early (release from heme catabolism) and late (release from RE stores) phases depended on the size of RE iron stores, as illustrated by the inverse relationship observed between early release and plasma ferritin (P less than .001). There was a strong correlation between early release and the rate of change of serum iron levels during the first three hours in normal subjects (r = .85, P less than .001). Inflammation produced a blockade of the early release phase, whereas in idiopathic hemochromatosis early release was considerably increased as compared with subjects with similar iron stores. Based on these results, we describe a model of RE iron metabolism in humans. We conclude that the RE system appears to determine the diurnal fluctuations in serum iron levels through variations in the immediate output of heme iron. In idiopathic hemochromatosis, a defect of the RE cell in withholding iron freed from hemoglobin could be responsible for the high serum iron levels and low RE iron stores.

We studied 24 recipients of autologous bone marrow transplantation (ABMT) or allogeneic BMT (BMT) to determine whether impaired erythropoietin (Epo) response to anemia could delay full erythropoietic recovery. Observed Epo levels were compared with predicted levels based on the relationship between Epo and hematocrit in 125 control subjects. Circulating Epo levels were normal during conditioning and the early posttransplant period. Between days 21 and 180, Epo levels remained normal in ABMT patients but were inappropriately low for the degree of anemia in BMT patients. Median time to full erythropoietic engraftment was longer in BMT than in ABMT recipients. Circulating Epo returned to appropriate levels after day 180, except in patients with active cytomegalovirus infection. We conclude that impaired Epo response to anemia can contribute to delayed erythropoietic recovery after allogenic BMT. Renal toxicity of ciclosporin, interaction between host and donor marrow, and cytomegalovirus infection might play a role. This study could support the use of recombinant human Epo to accelerate erythropoietic engraftment after BMT.

Background. It is now well established that after conventional allogeneic hematopoietic stem-cell transplantation (HSCT), erythropoietic recovery is impaired because erythropoietin (Epo) production remains inadequate for prolonged periods of time. However, erythropoietic reconstitution after nonmyeloablative SCT (NMSCT) has never been characterized.Methods. Twelve patients received a nonmyeloablative conditioning regimen consisting of 2 Gy total body irradiation (TBI) alone (n‫,)6؍‬ 2 Gy TBI and fludarabine (n‫,)3؍‬ or cyclophosphamide and fludarabine (n‫,)3؍‬ followed by transplantation of allogeneic peripheral blood stem cells. Graft-versus-host-disease (GvHD) prophylaxis was carried out with mycophenolate mofetil (from day ؊1 to day 28) plus cyclosporine (from day ؊1 to day 120 or longer in case of chronic GvHD). Erythropoiesis was quantitated by soluble transferrin receptor (sTfR) levels, and the adequacy of Epo production was evaluated by the observed-to-predicted Epo ratio (O/P Epo).Results. Mean sTfR levels decreased following the conditioning regimen but remained well within the normal range throughout the posttransplant period. The O/P Epo ratio presented an initial surge quite similar to that observed after conventional conditioning. Thereafter, the O/P Epo ratio normalized rapidly, and Epo levels remained adequate during the whole observation period. Conclusion.Contrarily to what is observed after myeloablative transplant, Epo levels remained adequate after NMSCT, resulting in normal erythropoiesis. These results suggest that the administration of erythropoietin therapy (rHuEpo) could be less effective after NMSCT than after conventional allogeneic transplant.

Recombinant human erythropoietin (rHuEpo) has been shown to be effective in correcting the anemia of chronic renal failure, but the dose needed may be variable. The reason for this variation is not known, but several factors could be involved, such as iron deficiency, inflammation, aluminum intoxication, hyperparathyroidism, blood losses, or marrow dysfunction. Treatment with rHuEpo was given intravenously thrice weekly after hemodialysis to 64 consecutive unselected patients with the anemia of chronic renal failure. The starting dose was 50 U/kg/dose, which was increased to 75 and 100 U/kg/dose if no response was observed after 1 and 2 months of treatment. After a minimum follow- up of 6 months, response was evaluated as early (hematocrit [Hct] > or = 30% before 3 months) or late (Hct > or = 30% after 3 months) response, or failure (target Hct not attained). We examined the value of various laboratory parameters (baseline values and early changes) as predictors of response to rHuEpo. The best prediction by pretreatment parameters only was obtained with baseline serum transferrin receptor (TfR) (< or > or = 3,500 ng/mL) and fibrinogen (< or > or = 4 g/L): 100% response rate when both parameters were low, versus only 29% when they were both high, and versus 67% when one was low and the other high. When the 2-week TfR increment was greater than 20%, the response rate was 96%. When TfR increment was less than 20%, the response rate was 100% when baseline TfR and fibrinogen were low, 12% when fibrinogen was elevated, and 62% when fibrinogen was low but baseline TfR high. The predictive value of baseline TfR and fibrinogen and of the 2-week increment of TfR was confirmed by life table analysis and stepwise discriminant analysis. Major reasons for failure or late response were identified and included subclinical inflammation, iron deficiency, functional iron deficiency, marrow disorders, hemolysis, bleeding, and low Epo dose. We conclude that response to rHuEpo can be predicted early by pretreatment fibrinogen and TfR, together with early changes of TfR levels. These prognostic factors illustrate the importance of the early erythropoietic response, subclinical inflammation, and functional iron deficiency. Early recognition of a low probability of response in a given patient could help identify and correct specific causes of treatment failure to hasten clinical improvement and avoid prolonged ineffective use of an expensive medication.