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Year : 2013  |  Volume : 26  |  Issue : 2  |  Page : 132-137

The role of soluble transferrin receptor in iron overload in children with chronic hemolytic anemia

1 Department of Pediatrics, Faculty of Medicine, Menoufia University, Menufia, Egypt
2 Department of Clinical Pathology, Faculty of Medicine, Menoufia University, Menufia, Egypt

Date of Submission12-Feb-2013
Date of Acceptance25-Jun-2013
Date of Web Publication31-Jan-2014

Correspondence Address:
Reda I Rakha
MBBCh, Kotur, Gharbia
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1110-2098.126144

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The current study was conducted to study the pathophysiology of iron overload in children with chronic hemolytic anemia (thalassemia major, thalassemia intermedia, and sickle cell anemia) and to assess the utility of soluble transferrin receptor (sTfR) for the evaluation of iron overload.
Iron overload is a major complication of repeated blood transfusion in patients with chronic hemolytic anemia. sTfR, one of the main regulators of cellular iron homeostasis, is the truncated form of the tissue receptor.
Patients and methods
Sixty children with chronic hemolytic anemia (20 thalassemia major, 20 thalassemia intermedia, and 20 sickle cell anemia) were included, together with 20 age-matched and sex-matched controls. Clinical evaluation was performed for each child. Complete blood count along with serum ferritin and sTfR levels (using the ELISA technique) was assessed for both patients and controls.
Both serum ferritin and sTfR levels were significantly higher in patients (2109±1350 ng/dl and 4.5±1.1 μg/ml, respectively) compared with controls and in patients with thalassemia major compared with those with thalassemia intermedia and those with sickle cell disease. Serum ferritin and sTfR levels were significantly correlated with age and with each other. Each of them negatively correlated with age at disease onset, time space between blood transfusions, and with hemoglobin level.
The sTfR level could contribute to and be used for the evaluation of iron overload in children with thalassemia and sickle cell disease.

Keywords: Iron overload, sickle cell anemia, soluble transferrin receptor, thalassemia

How to cite this article:
El-Rashidi FH, El-Nemr FM, Ragab SM, El-Din Fathallah SM, Rakha RI. The role of soluble transferrin receptor in iron overload in children with chronic hemolytic anemia. Menoufia Med J 2013;26:132-7

How to cite this URL:
El-Rashidi FH, El-Nemr FM, Ragab SM, El-Din Fathallah SM, Rakha RI. The role of soluble transferrin receptor in iron overload in children with chronic hemolytic anemia. Menoufia Med J [serial online] 2013 [cited 2020 Feb 23];26:132-7. Available from: http://www.mmj.eg.net/text.asp?2013/26/2/132/126144

  Introduction Top

Hemolytic anemia is anemia due to reduced life span of red blood cells either in the blood vessels (intravascular hemolysis) or elsewhere in the body (extravascular hemolysis) [1] .

Thalassemia syndromes are heterogenous groups of inherited anemias characterized by defects in the synthesis of one or more of the globin chain subunits of the hemoglobin (Hb) tetramer [2] . Decreased production or absence of one globin chain (α or μ) and a relative excess of the other lead to unpaired globin chains that precipitate and cause premature death of the red cell precursors within the marrow, termed as ineffective erythropoiesis [3] .

Sickle cell disease (SCD) and its variants are genetic disorders of mutant Hb. Sickle cell anemia is caused by a point mutation in the μ-globin chain of hemoglobin, causing glutamic acid to be replaced with valine at the sixth position. Under low-oxygen conditions (being at high altitude, for example), the absence of a polar amino acid at position six of the μ-globin chain promotes aggregation of Hb, which distorts red blood cells into a sickle shape and decreases their elasticity [4] .

In some disorders such as μ-thalassemia, excessive intestinal absorption also adds to the transfusion-induced iron overload. In thalassemia intermedia, a high erythropoietic drive causes hepcidin deficiency. The lack of hepcidin results in hyperabsorption of dietary iron and body iron overload. In contrast, in thalassemia major, transfusions decrease the erythropoietic drive and increase the iron load, resulting in relatively higher hepcidin levels. In the presence of higher hepcidin levels, dietary iron absorption is moderated and macrophages retain iron, but body iron stores increase due to the inability to excrete iron in transfused red blood cells [5] .

Major organs affected by iron overload include the heart, lung, liver, and endocrine glands.

Cardiac involvement is a major determinant of prognosis in iron-overload states. Hypertrophy and dilatation are common [6] .

Pulmonary hypertension appears to be less common in thalassemia major patients who undergo transfusion, probably because of the correction of hypoxia, whereas it is more common in the less transfused thalassemia intermedia patients [7] .

Liver involvement is common in those who undergo long-term transfusions. Early cirrhotic changes can be observed as early as 7 years of age in some people with thalassemia. Once cirrhosis develops, the risk for hepatocellular carcinoma is increased [8] .

Endocrine dysfunction affects virtually all glands. Pituitary involvement causes delayed puberty in more than 50% of patients. Up to 14% may develop insulin-dependent diabetes mellitus. Even those without diabetes have impaired insulin secretion. Thyroid, parathyroid, and exocrine pancreas are also affected [9] .

Iron transport in the plasma is carried out by transferrin, which donates iron to cells through its interaction with a specific membrane receptor. The transferrin receptor (TfR) is a 760-amino-acid glycoprotein. Virtually all cells, except mature red cells, have TfR on their surface, but the largest numbers are present in the erythron, placenta, and liver. In a normal adult, about 80% of TfR is present in the erythroid marrow [10] .

A circulating form of TfR has been found in human and animal serum. Serum soluble transferrin receptor (sTfR) is a soluble truncated monomer of tissue receptor, lacking its first 100 amino acids, which circulates in the form of a complex of transferrin and its receptor [11] .

sTfR is produced by proteolysis, mediated by a membrane-associated serine protease that occurs mostly at the surface of exosomes within the multivesicular body before exocytosis [12] .

Increased sTfR levels are seen in situations of stimulated erythropoiesis, such as congenital dyserythropoietic anemia, hemolytic anemia, hereditary spherocytosis, sickle cell anemia, thalassemia major or intermedia, megaloblastic anemia, or secondary polycythemia [13] .

Evaluation of marrow erythropoietic activity by sTfR is valuable in patients receiving chronic transfusions. Measurements of sTfR levels have demonstrated that patients who undergo blood transfusions at regular intervals show better marrow suppression compared with those who are transfused more sporadically [14] .

  Patients and methods Top


This study was carried out at the Pediatrics Department, Hematology and Oncology Unit and Clinical Pathology Department, Faculty of Medicine, Menoufia University. This study has been approved by ethical committee, informed consent have been taken from the caregivers of the included children.

Cases were divided into three groups:

First group: Patients with thalassemia major (n=20) (14 boys and six girls) with a mean age of 12 ± 6 years.

Second group: Patients with thalassemia intermedia (n=20) (13 boys and seven girls) with a mean age of 10 ± 5 years.

Third group: Patients with SCD (n=20) (16 boys and four girls) with a mean age of 8 ± 5 years.

The third group included 14 patients with sickle cell anemia and six patients with sickle thalassemia.

At the time of sampling, all patients were in stable disease condition; that is, they had no intercurrent infection and no crises.

Control group: Apparently healthy children (n=20) (11 boys and nine girls) with mean age of 9 ± 4 years.


Peripheral blood samples were drawn from each child. Each sample was divided into two portions: the first part was collected in a tube containing EDTA and used for determining the complete blood count, whereas the second part was collected in a plain tube, left to clot, centrifuged, and the serum separated and stored at −80°C for later use. Serum sTfR was quantitatively determined by enzyme linked immunoassay using monoclonal antibodies specific for sTfR using a kit manufactured by BioVendor Research and Diagnostic Products [Version 41021009 15; Heidelberg, Germany; catalogue number: RD 194011100 (IVD)]. The reference ranges were 1.0-2.9 μg/ml [15] .

Statistical analysis

Analysis of data was carried out using an IBM computer utilizing statistical program for social science (version 18.0; Chicago, Illinois, USA). Description of quantitative variables was given as mean, SD, and range. The χ2 -test was used to compare qualitative variables between groups. The unpaired t-test was used to compare quantitative variables in parametric data. The Mann-Whitney test was used instead of the unpaired t-test for nonparametric data. The ANOVA test was used for comparison of quantitative data among different time points in the same group. P values less than 0.05 were considered significant and P values less than 0.01 were considered highly significant [16] .

  Results Top

Symptoms of thalassemia major manifest earlier than those of thalassemia intermedia and sickle cell anemia.

Patients with thalassemia major undergo frequent blood transfusions compared with patients with thalassemia intermedia or sickle cell anemia.

There is a significantly high use of iron chelator among the thalassemia groups compared with the sickle cell anemia group.

There was an increase in the incidence of splenectomy in the diseased groups - six in thalassemia intermedia (30%), 11 in thalassemia major (55%), and six in sickle cell anemia (30%) - and an increased incidence of splenomegaly - 11 in thalassemia intermedia (55%), nine in thalassemia major (45%), and nine in sickle cell anemia (45%) [Table 1].
Table 1: Comparison between thalassemia major, thalassemia intermedia, and sickle cell anemia patients with respect to clinical data

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There was an increased incidence of hepatomegaly in all diseased groups: 13 in thalassemia intermedia (65%), 15 in thalassemia major (75%), and 12 in sickle cell anemia (60%) [Table 1].

There were statistically high serum ferritin levels among all diseased groups (2109 ± 1350 ng/dl) compared with the control group (106 ± 23 ng/dl). The level of increase was highest in the thalassemia major group (3485 ± 1340 ng/dl), followed by the thalassemia intermedia (1791 ± 505 ng/dl) and sickle cell anemia (1050 ± 574 ng/dl) groups [Table 2] and [Table 3].
Table 2: Comparison between control and diseased groups with respect to laboratory data

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Table 3: Comparison between control, thalassemia major, thalassemia intermedia, and sickle cell anemia patients with respect to laboratory data

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There were statistically high sTfR levels among all diseased groups (4.5 ± 1.1 μg/ml) compared with the control group (2.1 ± 0.7 μg/ml). The level of increase was highest in the thalassemia major group (5.7 ± 0.7 μg/ml), followed by the thalassemia intermedia (4.4 ± 0.8 μg/ml) and sickle cell anemia (3.5 ± 0.4 μg/ml) groups [Table 2] and [Table 3].

There was a strong positive correlation between serum ferritin and sTfR in all diseased groups (P < 0.01) [Table 4] and [Figure 1].
Figure 1:

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Table 4: Correlation between soluble transferrin receptor and serum ferritin and other variables in the diseased group

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There was a strong negative correlation between sTfR and age at onset, Hb, and time space between transfusions in all diseased groups (P < 0.01) [Table 4] and [Figure 2].
Figure 2:

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  Discussion Top

The two major determinants of the level of sTfR are body iron status and bone marrow erythroid expansion and activity. Hence, there will be an increased synthesis of sTfR in conditions associated with increased erythropoietic activity [17] .

With respect to age at onset, symptoms and signs of hemolysis appear early in thalassemia major patients compared with thalassemia intermedia and sickle cell anemia patients. This is in agreement with the results of Aessopos et al. [18] .

A statistically significantly high incidence of splenomegaly was observed among the diseased groups: thalassemia major (45%), thalassemia intermedia (55%), and sickle cell anemia (45%). In addition, a statistically significant incidence of splenectomy was also observed among the diseased groups: thalassemia major (55%), thalassemia intermedia (30%), and sickle cell anemia (30%). This is in agreement with the results of Al-Salem et al. [19] who did a retrospective analysis on 143 patients who had hemolytic anemia; these disorders included SCD (100 patients), sickle thalassemia (13 patients), and thalassemia major (30 patients). Splenectomy in SCD, sickle thalassemia, and thalassemia major was observed in 40, 50, and 54% of children, respectively.

A statistically significant incidence of hepatomegaly was observed among diseased groups compared with controls, especially among thalassemic patients. This is in agreement with the results of Kohgo et al. [20] who stated that transfusion and chronic hemolytic disorders commonly lead to hepatic hemosiderin deposition. The liver is the most important organ for iron storage with the largest capacity to sequester excess iron in transfusion-dependent patients. Clinically, the liver is hardened and palpable, and serum transaminase levels are moderately elevated.

Thalassemia major patients underwent blood transfusions significantly more frequently and had significantly higher usage of iron chelators compared with both thalassemia intermedia and sickle cell anemia patients.

In the absence of a physiological mechanism for actively excreting excess iron, the ongoing accumulation of iron in thalassemic patients through increased dietary uptake, with or without transfusion therapy, will result in serious clinical sequelae; hence, effective management of iron overload by iron chelators is required [5] .

With regard to serum ferritin, there was a significantly elevated value among diseased groups compared with control (P < 0.01), with thalassemia major patients showing the highest levels (3485 ± 1340 ng/dl) compared with both thalassemia intermedia (1791 ± 505 ng/dl) and sickle cell anemia (1050 ± 574 ng/dl) patients. This is in agreement with the results of Brissot et al. [21] who found that, in the severe form of μ-thalassemia, multiple blood transfusions and deficiency of hepcidin, a potent iron absorption inhibitor, result in iron overload with increased serum ferritin concentration.

Similar to μ-thalassemia, there were elevated levels of serum ferritin in patients with sickle cell anemia compared with control. This is in agreement with the results of Koduri [22] who observed elevated serum ferritin in SCD as a result of increased red cell turnover.

Although serum ferritin levels are proportionate to the quantity of iron stored in the body, countless other genetic and acquired conditions, with and without iron overload, can influence the results. An increase in ferritin concentrations with no excess body iron can be observed in acute and chronic inflammatory processes, autoimmune diseases, neoplasia, chronic renal insufficiency, hepatopathies, and metabolic syndromes [23] .

With regard to sTfR, the level was significantly elevated among diseased groups compared with control (P < 0.01), and the highest value was observed in thalassemia major (5.7 ± 0.7 μg/ml) patients compared with both thalassemia intermedia (4.4 ± 0.8 μg/ml) and SCD (3.5 ± 0.4 μg/ml) patients. This denotes that the degree of ineffective erythropoiesis is high in the thalassemia major group compared with other groups.

Previous studies [24],[25],[26],[27],[28],[29] have demonstrated statistically higher levels of serum sTfR in patients with μ-thalassemia compared with the control group. This could be attributed to the increased erythropoietic activity in thalassemic patients.

As in μ-thalassemia, patients with sickle cell anemia had elevated serum sTfR compared with controls. In agreement with this, Lulla et al. [30] and Speeckaert et al. [31] showed that all patients with SCD had elevated serum sTfR levels due to the increased hemolysis and erythropoietic drive, and suggested that sTfR is primarily a biomarker for erythropoietic drive in SCD.

Tanno et al. [32] observed that thalassemia syndromes and sickle cell anemia, which are characterized by a high degree of ineffective erythropoiesis, anemia, and tissue hypoxia, lead to an elevation of GDF15 (the main hepcidin inhibitor), and inadequate hepcidin allows increased iron absorption, which participates in iron overload.

Serum hepcidin levels (which are suppressed in iron overload disorders) showed a significant inverse correlation with the markers of erythropoietic activity, such as the sTfR. In a study performed in vivo on physiological erythropoiesis focusing on the relationship between plasma hepcidin, GDF15, and sTfR, the results suggest that GDF15 contributes to hepcidin suppression and iron overload in the pathological setting of ineffective erythropoiesis, such as thalassemia syndromes and SCD [33] .

In this study, serum ferritin correlated to sTfR, and both correlated to age of the patient as well as to low Hb level, young age at onset, and short duration between red blood cell transfusions in diseased groups.

The presence of a negative correlation between serum ferritin and age at onset, time space between transfusions, and Hb means that the severe form of hemolysis presents early, necessitating more frequent blood transfusion, which causes a significant elevation in serum ferritin level as an indicator of iron overload.

Previous studies [27],[30] observed a significant negative correlation between sTfR concentration and Hb concentration in the whole μ-thalassemia group, both μ-thalassemia major and μ-thalassemia intermedia subgroups and the sickle cell anemia group. This means that anemia is a contributing factor for sTfR elevation.

The strong positive correlation between sTfR and serum ferritin reflects the link between them and proposed the role of sTfR as a determinant factor for iron overload in our patients.

The results of this study show that the highest levels of sTfR (reflecting the degree of ineffective erythropoiesis) and serum ferritin (iron overload) were observed in the thalassemia major group compared with other groups, suggesting that sTfR can be a mirror reflecting ineffective erythropoiesis and increase in iron absorption and hence increase in iron overload in these patients.

  Acknowledgements Top

Conflicts of interest

None declared.

  References Top

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  [Figure 1], [Figure 2]

  [Table 1], [Table 2], [Table 3], [Table 4]


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