Serum soluble transferrin receptor concentration is an accurate estimate of the mass of tissue receptors.

peer reviewedOBJECTIVE: Serum levels of the soluble transferrin receptor (sTfR) vary depending on the erythropoietic activity and iron status. In vitro, sTfR shed in the incubation medium correlates well with cellular TfR, but this relationship has never been established in vivo. To determine the value of serum sTfR as a quantitative marker of the body mass of tissue TfR, we designed experiments to examine the correlation between serum sTfR and tissue TfR in rats with various degrees of erythropoietic activity or iron status. MATERIALS AND METHODS: We studied changes in erythropoietic activity in normal rats as well as in animals experiencing hemolysis, phlebotomy-induced iron deficiency, transfusion- or thiamphenicol-induced erythroid aplasia, or inflammation. At the end of follow-up, ferrokinetic studies were performed and animals were sacrificed. Organs were isolated and homogenized to determine the total mass of tissue TfR from the sum of tissue solubilized TfR in the bone marrow, spleen, liver, and blood cells (direct method). An indirect method was developed to derive the corporeal mass of tissue TfR from a representative marrow sample. RESULTS: As expected, serum sTfR and total mass of tissue TfR varied as a function of iron status and erythropoiesis. Relative erythroid expansion in the spleen was greater than in the bone marrow. With the exception of phlebotomized animals, the indirect method correlated very well with direct measurements of the total mass of tissue TfR (r = 0.97, p < 0.0001). There was a close relationship between the total mass of tissue TfR and the total mass of serum sTfR (r = 0.79, p < 0.0001). Serum sTfR represented approximately 5-6% of the total mass of tissue TfR in most experimental situations, but this ratio was twice as high during iron-restricted erythropoiesis. In addition, the ratio could be higher or lower in nonsteady-state situations, because changes in tissue TfR occurred faster than those of serum sTfR. CONCLUSIONS: Serum sTfR represents a constant proportion of the total mass of tissue TfR over a wide range of erythropoietic activity. However, iron deficiency results in a higher proportion of serum sTfR, and the pace of change in serum sTfR levels is slower than that of tissue TfR mass

Reticulocyte transferrin receptor (TfR) expression and contribution to soluble TfR levels.

BACKGROUND AND OBJECTIVES: Transferrin receptor (TfR) expression in erythroid cells is regulated by a number of factors, including iron status and erythropoietin (Epo) stimulation. However, the impact of these factors on reticulocyte TfR expression in vivo has never been studied. A soluble form of TfR (sTfR) is present in serum in proportion to the mass of cellular TfR. Although sTfR shedding by reticulocytes and erythroblasts has been demonstrated in vitro, the contribution of reticulocyte TfR to serum sTfR has never been evaluated in vivo. DESIGN AND METHODS: We measured directly the total number of reticulocyte TfR in normal rats of different age and iron status, as well as in animals experiencing various conditions and treatments aimed at altering erythropoietic activity and iron status, including rHuEpo therapy, hemolytic anemia, phlebotomies, hypertransfusions, thiamphenicol-induced red cell aplasia or inflammation. In addition, we examined the impact of repeated hypertransfusions with normal, reticulocyte-poor and reticulocyte-rich blood on serum sTfR levels. RESULTS: The number of TfR molecules per reticulocyte was around 50,000 in young rats but was around 100,000 in older animals. These values remained constant in most conditions and in particular were not influenced by iron supplementation or iron overload. However, functional iron deficiency as well as rHuEpo therapy resulted in increased reticulocyte TfR expression. In addition, TfR numbers in reticulocytes were elevated in the early phase of recovery after acute hemolysis or red cell aplasia but normalized soon after. Hypertransfusion experiments clearly demonstrated that reticulocytes can contribute substantially to sTfR levels in vivo. INTERPRETATION AND CONCLUSIONS: TfR numbers are regulated in vivo by the same factors as in vitro, in particular iron deficiency and erythropoietin stimulation. Circulating reticulocytes contribute significantly to serum sTfR levels

Anaemia of lung cancer is due to impaired erythroid marrow response to erythropoietin stimulation as well as relative inadequacy of erythropoietin production.

Many studies have been done in order to elucidate the pathogenesis of the anaemia of chronic disorders accompanying cancer, with conflicting results. This is probably due to the heterogeneity of the patient population selected for these studies (many patients treated by chemotherapy). To avoid this pitfall, in this study a very homogenous group of chemotherapy and radiotherapy-naive patients with lung cancer were selected. Serum erythropoietin and soluble transferrin receptor measurements suggested that the anaemia of non-treated lung cancer is mainly due to an impaired erythroid marrow response to erythropoietin stimulation. However, a relative inadequacy of erythropoietin production may also contribute

Monitoring of erythropoiesis by serum transferrin receptor levels in a case of chronic lymphocytic leukaemia and pure red cell aplasia treated with ciclosporin.

The authors present the case of a patient with chronic lymphocytic leukaemia complicated by pure red cell aplasia. Successful treatment with ciclosporin was facilitated by assay of serum transferrin receptor, which demonstrated a prompt and sustained response of marrow erythropoiesis to this therapy

Early prediction of response to recombinant human erythropoietin in patients with the anemia of renal failure by serum transferrin receptor and fibrinogen.

peer reviewedRecombinant 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 = 3,500 ng/mL) and fibrinogen ( 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

Quantitative assessment of erythropoiesis in haemodialysis patients demonstrates gradual expansion of erythroblasts during constant treatment with recombinant human erythropoietin.

Recombinant human erythropoietin (rHuEpo) has been shown to be effective in correcting the anaemia of chronic renal failure. It has been reported that reticulocytes as well as erythroid progenitors increase within 1-2 weeks, with no further elevation beyond this time interval. However, the erythroblast pool is quantitatively the most important compartment of erythropoiesis, and the rate, extent and duration of the expansion of erythropoietic activity in response to rHuEpo is not known. Treatment with rHuEpo was given to 64 patients i.v. thrice weekly after haemodialysis. The effect of rHuEpo was obvious from the early elevation of reticulocyte counts, but much of this increase was due to a rapid output of shift reticulocytes which levelled off after a few weeks. Serum transferrin receptor (TfR), a quantitative measure of erythropoiesis, increased progressively over 6 weeks to reach a plateau phase at about twice baseline values. The Hct increased progressively and continued to rise steadily after the TfR plateau was reached. The speed and extent of the expansion of erythropoietic activity correlated with the later haematological response to rHuEpo. When rHuEpo was discontinued, erythropoietic activity returned progressively to baseline values, to rise again gradually when treatment was resumed. Part of the Hct increase was also due to haemoconcentration. The results indicate that changes in the various erythroid compartments vary considerably in intensity and speed, and that the erythroblast compartment in particular is slow to respond to modifications in the erythropoietin stimulus

RISK OF RED BLOOD CELL ALLOIMMUNISATION IN RWANDA : ASSESSMENT OF PRETRANSFUSION CROSSMATCH TECHNIQUES USED IN DISTRICT HOSPITALS

Background: Screening of alloantibodies in patients is not yet done in district hospitals of Rwanda. The practice is to transfuse ABO/D compatible blood following an immediate spin crossmatch (IS-XM) or indirect antiglobulin test crossmatch (IAT-XM).Objectives: To assess the risk of red blood cell (RBC) alloimmunisation associated with the use of IS-XM compared to the IAT-XM in patients receiving blood transfusions in district hospitals in Rwanda.Design: A cross-sectional comparative descriptive study.Setting: Four Rwandan district hospitals. Kirehe and Nyanza hospitals used IS-XM while Muhima and Ruhengeri hospitals used IAT-XM.Subjects: Blood samples were obtained from 187 patients (101 with IS-XM and 86 with IAT-XM) transfused in January, February, October, and November of 2012.Results: The median age of blood recipients was 31 years (7 - 80) and 36% of them were male. Sixteen specific antibodies were identified in 12 patients: anti-RH1/D (2),anti-RH2/C (2), anti-RH3/E (2),anti-RH4/c  (1),anti-RH5/e (2),anti-LE1/Lea (2),anti-JK1/Jka (1),anti-JK2/Jkb (1),anti-KEL1/K (1),anti-MNS1/M (1),and autoantibody (1).The global prevalence of red blood cell (RBC) alloimmunisation was 6.4 % (12/187). That  prevalence was significantly higher in the IS-XM group (10.4%) than in the IAT-XM group (2.3%) with an odds ratio of 4.8; [95% CI=1.2-19.8]; and a p-value of 0.031.Conclusion: The prevalence of red blood cell (RBC) alloimmunisation in 187 patients receiving blood transfusions was 6.4% and was higher in recipients from hospitals using IS-XM, with Rhesus (RH) system antibodies widely predominant (56.2%).We recommend that IAT-XM be used in all district hospitals in Rwanda to minimise this risk