Erythroblast iron metabolism in sideroblastic and sideropenic states

Iron appears to exert self-regulatory control over erythroblast iron uptake, iron storage and its incorporation into haem. It does this via iron regulatory proteins (IRPs) which bind reversibly to the iron responsive elements (IREs) on the mRNA of transferrin receptor (TfR), erythroid 5-aminolaevulinic acid synthase (ALA-S2) and ferritin. Iron deficiency leads to the binding of IRP to IRE. This binding inhibits the translation of mRNA for ALA-S2 and ferritin but stabilizes mRNA for TfR expression. Sideroblastic erythropoiesis is highly ineffective and characterized by mitochondrial iron loading. The study of X-linked sideroblastic anaemia has shown that the entry of iron into the mitochondria is poorly controlled and able to occur when protoporphyrin production is reduced, as is seen with the ALA-S2 mutations, or when it is increased as has been seen with ABC7 transporter mutations. Sideropenia characterises both iron deficiency anaemia (IDA) and the anaemia of chronic disease (ACD). Erythroblasts in ACD seem doubly equipped to protect their iron supply with their ability to increase the efficiency of transferrin-iron uptake as well as to activate the IRP/IRE system to increase surface TfR production. This increase in efficiency restricts the need to increase surface TfR production and maintains serum soluble TfR (sTfR) values within the normal range in iron replete ACD. The coexistence of iron deficiency with chronic disease, however, is associated with an increase in both the efficiency and number and a highly significant rise in sTfR values.     

Erythroblast Iron Metabolism in Sideroblastic and Sideropenic States

Iron appears to exert self-regulatory control over erythroblast iron uptake, iron storage and its incorporation into haem. It does this via iron regulatory proteins (IRPs) which bind reversibly to the iron responsive elements (IREs) on the mRNA of transferrin receptor (TfR), erythroid 5-aminolaevulinic acid synthase (ALA-S2) and ferritin. Iron deficiency leads to the binding of IRP to IRE. This binding inhibits the translation of mRNA for ALA-S2 and ferritin but stabilizes mRNA for TfR expression.

Sideroblastic erythropoiesis is highly ineffective and characterized by mitochondrial iron loading. The study of X-linked sideroblastic anaemia has shown that the entry of iron into the mitochondria is poorly controlled and able to occur when protoporphyrin production is reduced, as is seen with the ALA-S2 mutations, or when it is increased as has been seen with ABC7 transporter mutations.

Sideropenia characterises both iron deficiency anaemia (IDA) and the anaemia of chronic disease (ACD). Erythroblasts in ACD seem doubly equipped to protect their iron supply with their ability to increase the efficiency of transferrin-iron uptake as well as to activate the IRP/IRE system to increase surface TfR production. This increase in efficiency restricts the need to increase surface TfR production and maintains serum soluble TfR (sTfR) values within the normal range in iron replete ACD. The coexistence of iron deficiency with chronic disease, however, is associated with an increase in both the efficiency and number and a highly significant rise in sTfR values.     

贫血患者血清转铁蛋白受体测定的临床意义

采用Ｄｏｔ－ＥＬＩＳＡ法定量测定了６８例不同贫血患者的血清转铁蛋白受体（ｓＴＩＲ）水平,发现缺铁性贫血,溶血性贫血和急性失血性贫血患者ｓＴＩＲ均显高于正常人（Ｐ〈０．００１）,而慢性再生障碍性贫血患者ｓＴｆＲ显著低于正常人（Ｐ〈０．００１）,缺铁性贫血ｓＴｆＲ水平与血清铁蛋白水平呈负相关（Ｐ〈０．００５）,溶血性贫血ｓＴｆＲ与网织红细胞计数呈正相关（Ｐ〈０．００５）,ｓＴｆＲ可以反映机体贮存铁和骨     

Single value of serum transferrin receptor is not diagnostic for the absence of iron stores in anaemic patients with rheumatoid arthritis

Serum transferrin receptor (sTfR) concentrations were measured in anaemic patients with rheumatoid arthritis (RA). Serum transferrin receptor concentrations were positively correlated with the percentage of hypochromic cells and negatively correlated with MCH. There was a weak correlation with serum ferritin (sFn) concentration but not with reticulocyte count. Thus, high concentrations of sTfR indicate iron-deficient erythropoiesis rather than levels of storage iron in the tissues. Patients were divided into three groups on the basis of sFn concentration: those with probable tissue iron deficiency, those with adequate iron stores and those with intermediate values of sFn which did not allow classification. The median sTfR concentration was significantly higher in the iron-deficient group than in the other two groups but because of overlap between the three groups, a single sTfR value was of limited value in determining the level of storage iron in an individual with RA.     

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

OBJECTIVE: 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.     

Factor V Leiden mutation carriership and venous thromboembolism in polycythemia vera and essential thrombocythemia

The aim of the present study is to evaluate in an elderly hospitalized population the diagnostic value of the serum transferrin receptor (sTfR) in distinguishing IDA (iron deficiency anemia) from ACD (anemia of chronic disease) as compared to conventional laboratory tests of iron metabolism, especially serum ferritin. In a prospective study, 34 patients with IDA and 38 patients with ACD (a chronic disorder in 23 and an acute infection in 15) were evaluated using iron status tests including serum transferrin receptor assay. The iron stores were assessed by bone marrow examination. sTfR levels were elevated (>28.1 nmol/L) in 68% of the IDA patients but also in 43% of the patients with ACD-chronic inflammation and 33% with ACD-acute infection. Serum ferritin was the best test to differentiate IDA from ACD patients. We conclude that serum ferritin is a more sensitive and specific parameter than the sTfR assay to predict the bone marrow iron status in an elderly anemic population.     

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.     

Defective iron supply for erythropoiesis and adequate endogenous erythropoietin production in the anemia associated with systemic-onset juvenile chronic arthritis

Systemic-onset juvenile chronic arthritis (SoJCA) is associated with high levels of circulating interleukin-6 (IL-6) and is frequently complicated by severe microcytic anemia whose pathogenesis is unclear. Therefore, we studied 20 consecutive SoJCA patients with hemoglobin (Hb) levels <12 g/dL, evaluating erythroid progenitor proliferation, endogenous erythropoietin production, body iron status, and iron supply for erythropoiesis. Hb concentrations ranged from 6.5 to 11.9 g/dL. Hb level was directly related to mean corpuscular volume (r = .82, P < .001) and inversely related to circulating transferrin receptor (r = - .81, P < .001) suggesting that the severity of anemia was directly proportional to the degree of iron-deficient erythropoiesis. Serum ferritin ranged from 18 to 1,660 microgram/L and was unrelated to Hb level. Bone marrow iron stores wore markedly reduced in the three children investigated, and they also showed increased serum transferrin receptor and normal-to-high serum ferritin. All 20 patients had elevated IL-6 levels and normal in vitro growth of erythroid progenitors. Endogenous erythropoietin (epo) production was appropriate for the degree of anemia as judged by both the observed to predicted log (serum epo) ratio 10.95 +/- 0.12) and a comparison of the serum epo- Hb regression found in these subjects with that of thalassemia patients. Multiple regression analysis showed that serum transferrin receptor was the parameter most closely related to hemoglobin concentration: variation in circulating transferrin receptor explained 61% of the variation in Hb level (P < .001). In 10 severely anemic patients, amelioration of anemia following intravenous iron administration resulted in normalization of serum transferrin receptor. Defective iron supply to the erythron rather than blunted epo production is the major cause of the microcytic anemia associated with SoJCA. A true body-iron deficiency caused by decreased iron absorption likely complicates long-lasting inflammation in the most anemic children, and this can be recognized by high serum transferrin receptor levels. Although oral iron is of no benefit, intravenous iron saccharate is a safe and effective means for improving iron availability for erythropoiesis and correcting this anemia. Thus, while chronically high endogenous IL-6 levels do not appear to blunt epo production, they are probably responsible for the observed abnormalities in iron metabolism. Anemia of chronic disease encompasses a variety of anemic conditions whose peculiar features may specifically correlate with the type of cytokine(s) predominantly released.     

Cessation of intensive treatment with recombinant human erythropoietin is followed by secondary anemia

Little information is available on the evolution of erythropoiesis after interruption of recombinant human erythropoietin (rHuEpo) therapy. Iron-overloaded rats received 20 daily injections of rHuEpo. During treatment, reticulocytes, soluble transferrin receptor (sTfR), and hematocrit increased progressively. This was accompanied by a substantial expansion of spleen erythropoiesis but a decrease in the bone marrow. Five weeks after treatment, rats developed a significant degree of a regenerative anemia. Erythropoietic activity, as assessed by reticulocytes, sTfR, erythroid cellularity, iron incorporation into heme, and the number of erythroid colonies, was severely depressed 3 weeks after cessation of rHuEpo. This was followed by regeneration of erythroblasts and reticulocytes at weeks 6 to 7 post-Epo, but erythroid progenitors recovered only partially by that time. The anemia was definitely corrected 2 months after cessation of rHuEpo treatment. Serum Epo levels remained elevated for several weeks, but the sensitivity of marrow erythroid precursors to Epo was preserved. No rat antibodies to rHuEpo were detected, and serum from post-Epo animals did not exert any inhibitory activity on erythropoiesis. In conclusion, after cessation of intensive rHuEpo therapy, there was a strong inhibition of erythropoietic activity with secondary anemia followed by late recovery. This was not due to antibodies or other soluble inhibitory factors, a defect in endogenous Epo production, or a loss of sensitivity to Epo. This may rather represent intrinsic erythroid marrow exhaustion, mostly at the level of erythroid progenitors but also at later stages of erythropoiesis.     

Late stage erythroid precursor production is impaired in mice with chronic inflammation

Background

We and others have shown previously that over-expression of hepcidin antimicrobial peptide, independently of inflammation, induces several features of anemia of inflammation and chronic disease, including hypoferremia, sequestration of iron stores and iron-restricted erythropoiesis. Because the iron-restricted erythropoiesis evident in hepcidin transgenic mice differs from the normocytic, normochromic anemia most often observed in anemia of inflammation, we tested the hypothesis that chronic inflammation may contribute additional features to anemia of inflammation which continue to impair erythropoiesis following the acute phase of inflammation in which hepcidin is active.

Design and Methods

We compared erythropoiesis and iron handling in mice with turpentine-induced sterile abscesses with erythropoiesis and iron handling in hepcidin transgenic mice. We compared erythrocyte indices, expression of genes in the hepcidin regulatory pathway, tissue iron distribution, expression of heme and iron transport genes in splenic macrophages, the phenotype of erythroid maturation and chloromethyl dichlorodihydrofluorescein diacetate, acetyl ester fluorescence.

Results

Mice with sterile abscesses exhibited an intense, acute inflammatory phase followed by a mild to moderate chronic inflammatory phase. We found that erythrocytes in mice with sterile abscesses were normocytic and normochromic in contrast to those in hepcidin transgenic mice. We also observed that although hypoferremia resolved in the late phases of inflammation, erythropoiesis remained suppressed, with evidence of inefficient maturation of erythroid precursors in the bone marrow of mice with sterile abscesses. Finally, we observed increased oxidative stress in erythroid progenitors and circulating erythrocytes of mice with sterile abscesses which was not evident in hepcidin transgenic mice.

Conclusions

Our results suggest that chronic inflammation inhibits late stages of erythroid production in the turpentine-induced sterile abscess model and induces features of impaired erythropoiesis which are distinct from those in hepcidin transgenic mice.Key words: anemia, inflammation, erythroid precursor, mouse models     

Altered erythropoiesis and iron metabolism in carriers of thalassemia

The thalassemia syndromes (α‐ and β‐thalassemia) are the most common and frequent disorders associated with ineffective erythropoiesis. Imbalance of α‐ or β‐globin chain production results in impaired red blood cell synthesis, anemia, and more erythroid progenitors in the blood stream. While patients affected by these disorders show definitive altered parameters related to erythropoiesis, the relationship between the degree of anemia, altered erythropoiesis, and dysfunctional iron metabolism has not been investigated in both α‐thalassemia carriers (ATC) and β‐thalassemia carriers (BTC). Here, we demonstrate that ATC have a significantly reduced hepcidin and increased soluble transferrin receptor levels but relatively normal hematological findings. In contrast, BTC have several hematological parameters significantly different from controls, including increased soluble transferrin receptor and erythropoietin levels. These changes in both groups suggest an altered balance between erythropoiesis and iron metabolism. The index sTfR/log ferritin and (hepcidin/ferritin)/sTfR are, respectively, increased and reduced relative to controls, proportional to the severity of each thalassemia group. In conclusion, we showed in this study, for the first time in the literature, that thalassemia carriers have altered iron metabolism and erythropoiesis.     

Expression and extracellular release of transferrin receptors on erythropoiesis

One of the most important factors for the proliferation and hemoglobin synthesis of erythroid cells is iron atom. This atom is tightly bound to serum transferrin (Tf) and is taken up by erythroblasts and reticulocytes through transferrin receptor (TfR). Both Tf and TfR are reutilizable and have roles for the efficient intracellular accumulation of iron. In addition to the reutilization (recycling), the expression of TfR is also regulated by cytoplasmic iron concentration; the increase of iron downregulate the synthesis of TfR at the translational level and vice versa. This mechanism was recently explained by the binding between "iron responsive element (IRE)" in the 5' end of TfR mRNA and IRE binding protein by a transacting manner. Johnstone et al, and we found that TfR was externalized from sheep reticulocyte and human erythroleukemia cell, K562, respectively. Furthermore, we confirmed that this shed TfR was detected in blood and concluded that the quantitation of TfR in serum is a useful index for evaluating the erythropoiesis. The serum TfR was increased in iron deficiency anemia, hemolytic anemia and polycythemia and was decreased in aplastic anemia. In renal anemia, it was increased after the administration of erythropoietin (Epo). By the in vitro liquid culture of peripheral blood stem cells using interleukin 3 and Epo, it was found that soluble TfR was derived from the erythroblasts during the maturation process.     

Serum soluble transferrin receptor and the prediction of marrow aspirate iron results in a heterogeneous group of patients

Serum soluble transferrin receptor (sTfR) concentration has been evaluated in the diagnosis of iron deficiency in otherwise healthy individuals and in patients with rheumatoid arthritis, but has not been studied in a general population of patients with complicated clinical presentations. In this study, 145 anaemic patients with a variety of medical conditions undergoing diagnostic bone marrow aspiration for any reason were tested by a complete blood count, a panel of biochemical tests to evaluate iron status, bone-marrow aspirate iron stain, and serum sTfR concentration. Sixteen per cent lacked stainable iron in the marrow aspirate. All biochemical parameters differed significantly between patients with or without stainable marrow iron. The sTfR assay was significantly more sensitive but less specific than other iron status assays in identifying the absence of stainable iron. Logistic regression analysis demonstrated that only sTfR and ferritin contributed independently to the prediction of marrow iron status. Serum ferritin alone was highly specific but insensitive. A decision algorithm combining serum ferritin and sTfR was as sensitive as TfR and as specific as serum ferritin. The measurement of serum sTfR, especially in conjunction with serum ferritin, is a valuable addition to the existing methods for predicting the results of marrow aspirate iron stains.     

Improved differential diagnosis of anemia of chronic disease and iron deficiency anemia: a prospective multicenter evaluation of soluble transferrin receptor and the sTfR/log ferritin index

Anemia of chronic disease (ACD) and iron deficiency anemia (IDA) are the most prevalent forms of anemia and often occur concurrently. Standard tests of iron status used in differential diagnosis are affected by inflammation, hindering clinical interpretation. In contrast, soluble transferrin receptor (sTfR) indicates iron deficiency and is unaffected by inflammation. Objectives of this prospective multicenter clinical trial were to evaluate and compare the diagnostic accuracy of sTfR and the sTfR/log ferritin index (sTfR Index) for differential diagnosis using the automated Access® sTfR assay (Beckman Coulter) and sTfR Index. We consecutively enrolled 145 anemic patients with common disorders associated with IDA and ACD. Subjects with IDA or ACD + IDA had significantly higher sTfR and sTfR Index values than subjects with ACD (P < 0.0001). ROC curves produced the following cutoffs for sTfR: 21 nmol/L (or 1.55 mg/L), and the sTfR Index: 14 (using nmol/L) (or 1.03 using mg/L). The sTfR Index was superior to sTfR (AUC 0.87 vs. 0.74, P < 0.0001). Use of all three parameters in combination more than doubled the detection of IDA, from 41% (ferritin alone) to 92% (ferritin, sTfR, sTfR Index). Use of sTfR and the sTfR Index improves detection of IDA, particularly in situations where routine markers provide equivocal results. Findings demonstrate a significant advantage in the simultaneous determination of ferritin, sTfR and sTfR Index. Obtaining a ferritin level alone may delay diagnosis of combined IDA and ACD. Am. J. Hematol., 2011. © 2011 Wiley‐Liss, Inc.     

血清转铁蛋白受体对贫血患者鉴别诊断的临床意义

目的比较各项铁指标在慢性病贫血(ACD),缺铁性贫血(IDA)及ACD合并IDA中的变化规律,明确血清转铁蛋白受体(sTfR)的临床意义.方法设健康志愿者28例为对照组,同时设IDA组29例,ACD组 56例,分别进行血清铁(SI)、总铁结合力(TIBC)、运铁蛋白饱和度(TS)、血清铁蛋白(SF)及sTfR检测,并对26例慢性病患者做骨髓铁染色,根据sTfR值将ACD组分为(1)sTfR值正常组(ACD1组)27例(sTfR≤20.0 nmol/L ),(2)sTfR值升高组(ACD2组)29例(sTfR>20.0 nmol/L).结果 IDA组与其他各组相比,其中平均红细胞体积(68.0±11.3)fl为最小;SI、TS及SF值分别是(19.6±10.1) mg/L、(5.5±2.3)%和(4.3±2.8)μg/L,与对照组(81.7±30.6) mg/L、(27.0±12.0)%和(43.3±26.8) μg/L相比水平明显下降(P≤0.01);sTfR水平(67.2±40.3) nmol/L明显高于对照组(15.6±4.1) nmol/L,P≤0.01.ACD1组SF值(627.3±40.3) μg/L,明显高于其他各组(P≤0.01); SI(60.7±28.7) mg/L和TS(21.1±9.8)%与对照组差异无显著性(P>0.05),10例骨髓铁染色均无缺铁.ACD2组SF值(320.5±156.0) μg/L,高于对照组而低于ACD1组(P≤0.01),16例骨髓铁染色中14例显示铁缺乏,占88%.结论 sTfR值的升高有效地反映了体内铁缺乏状况,是诊断IDA更为敏感的指标,并且较少受慢性炎症性疾病的影响,可与ACD有效鉴别.     

The usefulness of serum transferrin receptor and ferritin for assessing anemia in rheumatoid arthritis: comparison with bone marrow iron study

OBJECTIVES: This study was aimed at investigating the usefulness of serum transferrin receptor (sTfR) and ferritin in anemic patients with rheumatoid arthritis (RA) compared with bone marrow storage iron and other tests for anemia. METHODS: Fifty-five anemic RA patients underwent anemia study. Bone marrow iron stain was performed in 18 patients. sTfR and serum ferritin levels were compared with bone marrow iron stores. RESULTS: (1) Mean sTfR concentration was 2.63+/-1.91 mg/L, (2) sTfR correlated with most indicators of anemia, (3) sTfR showed no correlation with CRP and ESR, whereas ferritin did, and (4) sTfR was higher in the "iron depleted" subgroup than in the "iron nondepleted" subgroup in bone marrow study. CONCLUSION: The measurement of sTfR and ferritin is useful in finding the cause of anemia in RA and is a possible substitute for invasive bone marrow iron study.     

Iron stores and serum transferrin receptor levels during recombinant human erythropoietin treatment of anemia in rheumatoid arthritis

Summary Ten rheumatoid arthritis (RA) patients with anemia of chronic disorders (ACD) were treated with recombinant human erythropoietin (r-Hu-Epo) using a dose of 250 U/kg s.c. 3 times a week for 6 weeks, in order to evaluate its effects on the anemia, iron stores, and serum-soluble transferrin receptor (sTfR) levels. All patients showed a rise in hemoglobin (Hb). Median Hb increased from 5.9 (5.5–7.0) at baseline to 6.7 (5.8–7.8) at 3 weeks and to 7.2 (5.9–8.5) mmol/l at 6 weeks during treatment. Ferritin levels decreased significantly during the 6 weeks, and five patients were iron deficient after 6 weeks of treatment. TfR levels increased significantly at 3 and 6 weeks during treatment.These preliminary findings may indicate that r-Hu-Epo is effective in improving ACD in RA. The sTfR rise may be explained by an increase in erythroid precursor cell mass or increased TfR expression and a decrease in tissue iron stores, although direct effects of Epo on TfR regulation cannot be excluded. Large double-blind studies with r-Hu-Epo in patients with RA and ACD are warranted.This study was supported in part by Boehringer, Mannheim, Germany and by theDeutsche Forschungsgemeinschaft, SFB 263     

The usefulness of serum transferrin receptor for discriminating iron deficiency without anemia in children

We determined serum transferrin receptor (sTfR), serum erythropoietin and hematologic and biochemical iron parameters in 251 healthy children. The levels of sTfR were significantly higher in children with storage iron deficiency but had a poor sensivity for recognizing iron deficiency without anemia. When ferritin values cannot accurately demonstrate the iron deficiency in children, the sTfR/ferritin ratio or sTfR-log ferritin is recommended to discriminate iron deficiency in the absence of anemia.