Soluble transferrin receptor in Aboriginal children with a high prevalence of iron deficiency and infection

OBJECTIVES: Aboriginal children in tropical Australia have a high prevalence of both iron deficiency and acute infections, making it difficult to differentiate their relative contributions to anaemia. The aims of this study were to compare soluble transferrin receptor with ferritin in iron deficiency anaemia (IDA), and to examine how best to distinguish the effect of iron deficiency from infection on anaemia. METHODS: We conducted a prospective study of 228 admissions to Royal Darwin Hospital in children from 6 to 60 months of age. Transferrin receptor concentrations were measured by a particle-enhanced immunoturbidimetric assay and ferritin by a microparticle enzyme immunoassay. RESULTS: On multiple regression, the best explanatory variables for haemoglobin differences (r2=33.7%, P<0.001) were mean corpuscular volume (MCV), red cell distribution width (RDW) and C-reactive protein (CRP); whereas transferrin receptor and ferritin were not significant (P>0.4). Using > or =2 abnormal indices (MCV, RDW, blood film)+haemoglobin <110 g/l as the reference standard for IDA, transferrin receptor produced a higher area under the curve on receiver operating characteristic curve analysis than ferritin (0.79 vs. 0.64, P<0.001) or the transferrin receptor-ferritin index (0.77). On logistic regression, the effect of acute infection (CRP) on haemoglobin was significant (P<0.001) at cut-offs of 105 and 110 g/l, but not at 100 g/l when only iron deficiency indicators (MCV, RDW, blood film) were significant. CONCLUSIONS: Transferrin receptor does not significantly improve the diagnosis of anaemia (iron deficiency vs. infection) over full blood count and CRP, but in settings with a high burden of infectious diseases and iron deficiency, it is a more reliable adjunctive measure of iron status than ferritin.     

Soluble transferrin receptor as a potential determinant of iron loading in congenital anaemias due to ineffective erythropoiesis

Congenital anaemias due to ineffective erythropoiesis may be associated with excessive iron absorption and progressive iron loading. We investigated whether the soluble transferrin receptor (TfR) level was related to the degree of iron overload in 20 patients with thalassaemia intermedia, six patients with congenital dyserythropoietic anaemia type II (CDA II) and four patients with X-linked congenital sideroblastic anaemia (XLSA). All but two patients had increased serum ferritin levels (median 601 microgram/l, range 105-2855 microgram/l). Multiple regression analysis showed that 62% (P < 0.0001) of the variation in serum ferritin was explained by age and by changes in soluble TfR.     

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.     

Reticulocyte haemoglobin content vs. soluble transferrin receptor and ferritin index in iron deficiency anaemia accompanied with inflammation

Ferritin concentration, as a parameter of iron status that is commonly used in the diagnosis of iron deficiency anaemia (IDA), often has limited values if the iron deficiency is accompanied by inflammatory disease. This study evaluated the value of reticulocyte haemoglobin content (CHr) and soluble transferrin receptor-ferritin index (sTfR/F) in the diagnosis of IDA and differential diagnosis of IDA and anaemia of chronic disease. The study included 66 nonanaemic individuals as controls, 86 patients with IDA divided into noninflammatory and inflammatory subgroups, and 32 patients with anaemia of chronic disease. Blood count, iron, transferrin saturation, total iron binding capacity, ferritin, C-reactive protein, sTfR and CHr were determined. Receiver operator characteristic curve analysis showed very high discriminating power for CHr, soluble transferrin receptor (sTfR) and sTfR/F in the diagnosis of IDA. In patients with anaemia of chronic disease these parameters showed no significant difference from the control. CHr and sTfR enabled recognition of iron deficiency and were not affected by acute phase reaction. They are sensitive markers of body iron status with additional value to conventional tests for the detection of iron deficiency.     

The ratio of serum transferrin receptor and serum ferritin in the diagnosis of iron status

Laboratory tests used in the diagnosis of iron status lack specificity in defining iron deficiency anaemia (IDA) and anaemia of inflammation (AI). The serum transferrin receptor (sTfR) may provide more information in this regard. The iron status of 561 pre-school children was determined and classified using the conventional measurements. The value of the concentration of sTfR, the ratio of sTfR (microg/ml) to LogSF (microg/l) (TfR-Index), and the Log of the ratio of sTfR (microg/l) to SF (microg/l)--(LogTfR:Fer ratio), in the classification of the iron status were determined by comparing their distributions across the classification of iron status. Although there were significant differences in sTfR and TfR-Index across the categories of iron status, there was considerable overlap. All subjects with iron deficiency had LogTfR:Fer ratio > 2.55, whereas in all subjects classified as AI it was < 2.55, thus clearly separating the two. The LogTfR:Fer ratio was not able to exclude IDA in the presence of inflammation. However, in cases of combined IDA and AI the LogTfR:Fer ratio was < 2.55 but increased to > 2.55 after resolution of the inflammation. This novel method of calculating the LogTfR:Fer ratio may provide a more precise classification of the iron status of children.     

Evaluation of reticulocyte haemoglobin content as marker of iron deficiency and predictor of response to intravenous iron in haemodialysis patients

Because serum ferritin and transferrin saturation (TS) have a limitation in estimating iron status in haemodialysis patients, the reticulocyte haemoglobin content (CHr) has been proposed as a new tool. We investigate the accuracy of CHr in comparison with conventional tests and the relationship between changes in CHr and haemoglobin levels after therapy. We selected 140 haemodialysis patients receiving rHuEPO and intravenous iron supplementation and measured their complete blood count, CHr and iron parameters. Iron deficiency was defined as a ferritin <100 microg/l and/or a TS <20%. Hb, CHr, ferritin and TS levels were determined 1 month after therapy. Fifty-three patients were iron deficient. CHr were distributed with 33.7 +/- 1.4 pg in the iron sufficient group and with 29.9 +/- 1.9 pg in the iron deficient group (P = 0.001). The cutoff value of CHr for detecting iron deficiency was <32.4 pg. In iron deficient patients, a significant correlation was found between CHr and TS. The change in CHr after therapy was significantly larger in iron-deficient patients, and a lower baseline CHr is associated with a greater haemoglobin change. CHr is useful in screening iron status in dialysis patients, and a CHr cut-off value of 32 pg is appropriate for the assessment of iron deficiency. Moreover, CHr may serve as a predictor of the response to anaemia treatment.     

Effect of repeated apotransferrin administrations on serum iron parameters in patients undergoing myeloablative conditioning and allogeneic stem cell transplantation

Myeloablative conditioning prior to allogeneic stem cell transplantation causes a rapid increase in transferrin saturation and potentially toxic non-transferrin-bound iron (NTBI) in plasma. We have studied the ability of repeatedly administered apotransferrin to maintain this iron in a transferrin-bound form. Twenty adult patients undergoing myeloablative conditioning and allogeneic stem cell transplantation were enrolled to receive apotransferrin with one of three dosage regimens. Ten consecutive patients with the same preconditioning were studied as controls. At the highest dose level, full transferrin saturation and appearance of NTBI were prevented in five of the eight patients. Serum iron increased significantly more in the patients receiving apotransferrin than in the controls and remained elevated until erythropoietic recovery. From the increment of iron saturation and the amount of endogenous and administered apotransferrin, an average 180 mumol of iron per day was bound to transferrin during the first 4 d after the start of the conditioning therapy. Thereafter, iron accumulation levelled off in most patients. The results suggested that about half of the amount of iron normally transported to erythropoiesis was initially released to plasma after induction of the erythroid arrest. Complete iron binding with apotransferrin would apparently require very high apotransferrin doses.     

The MCK mouse heart model of Friedreich's ataxia: Alterations in iron-regulated proteins and cardiac hypertrophy are limited by iron chelation

There is no effective treatment for the cardiomyopathy of the most common autosomal recessive ataxia, Friedreich's ataxia (FA). The identification of potentially toxic mitochondrial (MIT) iron (Fe) deposits in FA suggests that Fe plays a role in its pathogenesis. This study used the muscle creatine kinase conditional frataxin (Fxn) knockout (mutant) mouse model that reproduces the classical traits associated with cardiomyopathy in FA. We examined the mechanisms responsible for the increased cardiac MIT Fe loading in mutants. Moreover, we explored the effect of Fe chelation on the pathogenesis of the cardiomyopathy. Our investigation showed that increased MIT Fe in the myocardium of mutants was due to marked transferrin Fe uptake, which was the result of enhanced transferrin receptor 1 expression. In contrast to the mitochondrion, cytosolic ferritin expression and the proportion of cytosolic Fe were decreased in mutant mice, indicating cytosolic Fe deprivation and markedly increased MIT Fe targeting. These studies demonstrated that loss of Fxn alters cardiac Fe metabolism due to pronounced changes in Fe trafficking away from the cytosol to the mitochondrion. Further work showed that combining the MIT-permeable ligand pyridoxal isonicotinoyl hydrazone with the hydrophilic chelator desferrioxamine prevented cardiac Fe loading and limited cardiac hypertrophy in mutants but did not lead to overt cardiac Fe depletion or toxicity. Fe chelation did not prevent decreased succinate dehydrogenase expression in the mutants or loss of cardiac function. In summary, we show that loss of Fxn markedly alters cellular Fe trafficking and that Fe chelation limits myocardial hypertrophy in the mutant.     

Use of advanced red blood cell and reticulocyte indices improves the accuracy in diagnosing iron deficiency in pregnant women at term

Objectives: Detection of iron deficiency during pregnancy with hemoglobin (Hb) and serum measurements is insignificant as the measurements may be affected by e.g. hemodilution or accelerated erythropoiesis. This study tests whether cell indices will give a more reliable measure of iron deficiency in pregnant women at term. Methods: The population was 202 pregnant women. Using the ADVIA 120 hematology system, Hb, mean cell volume (MCV), percentage of hypochromic red blood cells (%HYPOm) and reticulocytes (%HYPOr), and cellular hemoglobin in reticulocytes (CHr) were tested. Additionally, transferrin saturation (TfSat), ferritin, and transferrin receptor (TfR) were analyzed. Receiver operating characteristic (ROC) curves and area under the ROC curves (AUC) were used as statistical methods. Results: When TfSat (≤11%) was used as the reference test for iron deficiency, %HYPOm and CHr had a sensitivity of 58.1% and 80.7%, while the specificities were 82.6% and 71.3%, respectively. Additionally, the AUC values were %HYPOr 0.80, CHr 0.79, ferritin 0.77, %HYPOm 0.75, TfR 0.67, MCV 0.63 and Hb 0.64. The results provided by the cell indices alone (%HYPOm or CHr) were in good agreement with the results based on the usage of a combination of three commonly used tests (Hb, MCV, ferritin). Conclusions: This study suggests that the most practical way to diagnose iron deficiency in pregnant women at term is to use cell indices such as CHr and %HYPOm provided by the automated hematological analyzer. Further studies are needed to determine the usefulness of the cell indices in diagnosing iron deficiency longitudinally during the course of pregnancy.     

Evaluation of reticulocyte parameters in iron deficiency, vitamin B(12) deficiency and beta-thalassemia minor patients

The aim of this study was to test the clinical utility of reticulocyte parameters in differential diagnosis in iron deficiency anemia (IDA), vitamin B(12) deficiency (B12) and beta-thalassemia minor (TM). We analyzed the percentage of reticulocyte, absolute reticulocyte count, mean content hemoglobin of reticulocyte (CHr), mean corpuscular volume of reticulocyte (MCVr), corpuscular hemoglobin concentration mean of reticulocyte (CHCMr), MCVr/MCV ratio, CHr/CH ratio and CHCMr/CHCM ratio in healthy donors (n = 34), iron deficiency (IDA) (n = 41), vitamin B(12) deficiency (B12) (n = 22), and TM (n = 34). This study demonstrates that the cutoff value of CHr was 25.7 as indicative of IDA (85.4% sensitivity, 97.1% specificity). CHr and MCVr may be useful for TM (cutoff value < or = 24.8 for CHr) and B12 (>102.1, cutoff value for MCVr), respectively. Sensitivity and specificity of these parameters were 90.9, 86.4% and 97.1, 82.4%, respectively. CHCMr is useful to differentiate IDA and TM from B12. While CHr was low value in microcytic groups (mean 21.8 +/- 3.3 for IDA, 21.0 +/- 2.9 for TM), it was high in B12 (mean 32.1 +/- 5.7). However, that of CHr/CH ratio was only significantly in IDA group compared with the control (P < 0.05, mean 0.98). Therefore, there are limitations regarding CHr and CHr/CH ratio differential diagnosis in microcytic and macrocytic groups. CHr, MCVr, and CHCMr are not sufficiently sensitive and specific to differentiate TM from IDA. We conclude that measurement of reticulocyte count and parameters may be a very useful implement in the diagnosis of IDA and TM.     

Transferrin receptor in proliferation of T lymphocytes in infants with iron deficiency

The aim of this study was to contribute to clarify the mechanism of cellular immune insufficiency occurring during iron deficiency. We studied the expression of the transferrin receptor (TfR) which is called as CD71, on the surface of T lymphocytes in infants with iron deficiency (with and without anemia). A total of 33 infants, aged between 7 and 26 months were included in this study. These subjects were divided into three groups: (i) latent iron deficiency (LID) (group 1), (ii) iron deficiency anemia (IDA) (group 2), and (iii) healthy infants (group 3). Both CD3 levels and CD71 expression of T lymphocytes were analysed by flow cytometry before and after phytohaemagglutinin (PHA) stimulation. The percentage of CD3(+) lymphocytes in infants with IDA was lower than that in controls after PHA stimulation (mean +/- SD, 48.6 +/-10.5% vs. 70.7 +/-7.8%, P < 0.001). The TfR expression of T lymphocytes (CD3 + CD71%) increased in all three groups after PHA stimulation (P < 0.001). No significant difference was seen among the three groups with respect to CD3 + CD71%. Although there was a reduction in the proliferative capacity of T lymphocytes in infants with IDA, their ability to express transferrin receptor on T-lymphocyte cell surface was normal.     

A critical role for murine transferrin receptor 2 in erythropoiesis during iron restriction

Effective erythropoiesis requires an appropriate supply of iron and mechanisms regulating iron homeostasis and erythropoiesis are intrinsically linked. Iron dysregulation, typified by iron‐deficiency anaemia and iron overload, is common in many clinical conditions and impacts the health of up to 30% of the world's population. The proteins transmembrane protease, serine 6 (TMPRSS6; also termed matriptase‐2), HFE and transferrin receptor 2 (TFR2) play important and opposing roles in systemic iron homeostasis, by regulating expression of the iron regulatory hormone hepcidin. We have performed a systematic analysis of mice deficient in these three proteins and show that TMPRSS6 predominates over HFE and TFR2 in hepcidin regulation. The phenotype of mice lacking TMPRSS6 and TFR2 is characterized by severe anaemia and extramedullary haematopoiesis in the spleen. Stress erythropoiesis in these mice results in increased expression of the newly identified erythroid iron regulator erythroferrone, which does not appear to overcome the hepcidin overproduction mediated by loss of TMPRSS6. Extended analysis reveals that TFR2 plays an important role in erythroid cells, where it is involved in terminal erythroblast differentiation and the regulation of erythropoietin. In conclusion, we have identified an essential role for TFR2 in erythropoiesis that may provide new targets for the treatment of anaemia.     

Serum transferrin receptor levels in patients undergoing evaluation of iron stores: correlation with other parameters and observed versus predicted results

Serum transferrin receptor (sTfR) concentrations were measured in specimens from 77 patients undergoing serum ferritin determination, and the results correlated with serum ferritin, serum iron, serum total iron-binding capacity (TIBC) saturation, erythrocyte mean corpuscular volume (MCV), and mean corpuscular haemoglobin (MCH). All parameters exhibited the expected inverse correlation with sTfR; this correlation was statistically significant for all parameters except serum iron concentration. The frequency with which iron deficiency (defined as absence of stainable marrow iron) is observed in patients with particular ferritin values in this centre was determined and used to estimate the expected number of iron deficient patients in the present study. In no setting were significantly fewer sTfR levels > 3.05 μg/ml observed than expected. However, significantly greater than expected numbers of elevated sTfR values were observed in patients with serum ferritin > 220 μg/l (P = 0.002). The results suggest that the sTfR level is probably not useful as a single test for identification of iron deficiency in unselected patients.     

Role of transferrin receptor 2 in hepatic accumulation of iron in patients with chronic hepatitis C

Background and Aim: Iron deposition in the liver is a common finding in patients with chronic hepatitis C (CH‐C). The mechanism of this hepatic accumulation of iron is not completely understood. This study assessed if the protein expression of transferrin receptor 2 (TfR2) is upregulated in the liver of patients with CH‐C and if TfR2 protein mediates iron accumulation during hepatitis C virus (HCV) infection. Method: Liver specimens from patients with CH‐C that underwent interferon (IFN) therapy (n = 23) and from patients with CH‐B (n = 18) were evaluated. Hepatic expression of TfR2 protein was analyzed by immunohistochemistry. Total hepatic iron score (THIS) was evaluated by Prussian blue staining. Results: TfR2 protein was expressed in the cell membrane and cytosol of hepatocytes. Cytosol TfR2 protein was found to co‐localize with Tf. THIS (P = 0.0198) and hepatic TfR2 (P = 0.0047) expression were significantly higher in CH‐C than in CH‐B. The change in THIS values (rho = 0.580, P = 0.0079) and the grade of histological activity (rho = 0.444, P = 0.0373) were significantly correlated with changes in TfR2 expression after IFN therapy. Conclusions: The protein expression of TfR2 is significantly associated with iron deposition in the liver in patients with CH‐C. HCV infection may affect the hepatic expression of TfR2, leading to iron accumulation in the liver.