Soluble transferrin receptor-transferrin complex in serum: measurement by latex agglutination nephelometric immunoassay

Influence of chronic training workload on the hematological profile: a pilot study in sedentary people, amateur and professional cyclists

Background and aim:

The assessment of hematological profile requires to identify possible sources of biological variability, including exercise-related variations. This study was hence aimed to evaluate hematological profile variations in amateur and professional athletes, and establish their possible dependence on cumulative training volume.

Materials and Methods:

The study population consisted of 59 sedentary male subjects, 78 amateur and 80 professional male cyclists, in whom a large number of hematological variables were measured at rest.

Results:

Red blood cell (RBC) count and hemoglobin were decreased in the two athlete cohorts compared to sedentary subjects, but did not differ between amateur and professional cyclists. Hematocrit was gradually and significantly decreased in parallel with cumulative training volume. Amateur cyclists displayed higher mean corpuscular volume (MCV) and lower mean corpuscular hemoglobin concentration (MCHC) values than sedentary subjects and professional cyclists, whilst mean corpuscular hemoglobin (MCH) was higher in professional cyclists. The reticulocyte count and soluble transferrin receptor (sTFR) values were similar across all groups. Serum ferritin was higher in professional cyclists than in the other two groups, whilst transferrin gradually decreased from sedentary group to the two cohorts of amateur and professional cyclists. In univariate analysis, cumulative training volume was inversely associated with age, body mass index (BMI), RBC count, hematocrit, hemoglobin and transferrin, whilst a positive association was found with ferritin. In multivariate analysis, BMI, RBC count and ferritin remained significantly associated with training volume.

Conclusions:

These results show that the volume of endurance training may affect some hematological variables. (www.actabiomedica.it)

Aggregation-Induced Emission Probe for Specific Turn-On Quantification of Soluble Transferrin Receptor: An Important Disease Marker for Iron Deficiency Anemia and Kidney Diseases

Transferrin receptor (TfR) is overexpressed on the surface of many cancer cells due to its vital roles in iron circulation and cellular respiration. Soluble transferrin receptor (sTfR), a truncated extracellular form of TfR in serum, is an important marker of iron deficiency anemia (IDA) and bone marrow failure in cancer patients. More recently, sTfR level in urine has been related to a specific kidney disease of Henoch-Schönlein purpura nephritis (HSPN). Despite the universal significance of sTfR, there is still a lack of a simple and sensitive method for the quantification of sTfR. Furthermore, it is desirable to have a probe that can detect both TfR and sTfR for further comparison study. In this work, we developed a water-soluble AIE-peptide conjugate with aggregation-induced emission (AIE) characteristics. Taking advantage of the negligible emission from molecularly dissolved tetraphenylethene (TPE), probe TPE-2T7 was used for the light-up detection of sTfR. The probe itself is nonemissive in aqueous solution, but it turns on its fluorescence upon interaction with sTfR to yield a detection limit of 0.27 μg/mL, which is much lower than the sTfR level in IDA patients. Furthermore, a proof-of-concept experiment validates the potential of the probe for diagnosis of HSPN by urine test.

Laboratory Assessment of Anemia

Anemia is one of the most common health problems in both industrialized and developing countries. It has been recognized by the World Health Organization as an important disorder leading to significant health care burden. Laboratory testing plays a significant role in the diagnosis of most types of anemia since the clinical diagnosis may not always be straightforward, especially with multiple underlying conditions. Once the existence of anemia is established, the cause must be determined to enable selection of a specific and effective therapy. Various hematologic parameters and biochemical tests can be used in combination with patient clinical history to identify the most likely causes of anemia.

Simultaneous assessment of iodine, iron, vitamin A, malarial antigenemia, and inflammation status biomarkers via a multiplex immunoassay method on a population of pregnant women from Niger

Deficiencies of vitamin A, iron, and iodine are major public health concerns in many low- and middle-income countries, but information on their status in populations is often lacking due to high costs and logistical challenges associated with assessing micronutrient status. Accurate, user-friendly, and low-cost analytical tools are needed to allow large-scale population surveys on micronutrient status. We present the expansion of a 7-plex protein microarray tool for the simultaneous measurement of up to seven biomarkers with relevance to the assessment of the key micronutrients iron, iodine, and vitamin A, and inflammation and malaria biomarkers: α-1-acid glycoprotein, C-reactive protein, ferritin, retinol binding protein 4, soluble transferrin receptor, thyroglobulin, and histidine-rich protein II. Assay performance was assessed using international reference standards and then verified by comparing the multiplexed and conventional immunoassay results on a training panel of plasma samples collected from US adults. These data were used to assign nominal concentrations to the calibrators of the assay to further improve performance which was then assessed by interrogating plasma samples from a cohort of pregnant women from Niger. The correlation between assays for each biomarker measured from this cohort was typically good, with the exception of thyroglobulin, and the sensitivity ranged from 74% to 93%, and specificity from 81% to 98%. The 7-Plex micronutrient assay has the potential for use as an affordable tool for population surveillance of vitamin A, iron, and iodine deficiencies as well as falciparum malarial parasitemia infectivity and inflammation. The assay is easy-to-use, requires minimal sample volume, and is scalable, rapid, and accurate—needing only a low-cost reader and basic equipment present in most reference laboratory settings and so may be employed by low and middle income countries for micronutrient surveillance to inform on status in key populations. Micronutrient deficiencies including iron, iodine, and vitamin A affect a significant portion of the world’s population. Efforts to assess the prevalence of these deficiencies in vulnerable populations are challenging, partly due to measurement tools that are inadequate for assessing multiple micronutrients in large-scale population surveys. We have developed a 7-plex immunoassay for the simultaneous measurement of seven biomarkers relevant to assessing iodine, iron, and vitamin A status, inflammation and Plasmodium falciparum parasitemia by measuring levels of thyroglobulin, ferritin, soluble transferrin receptor, retinol binding protein 4, α-1-acid glycoprotein, C-reactive protein, and histidine-rich protein II. This 7-plex immunoassay technique has potential as a rapid and effective tool for use in large-scale surveys and assessments of nutrition intervention programs in low- and middle-income countries.

Residual erythropoiesis protects against myocardial hemosiderosis in transfusion-dependent thalassemia by lowering labile plasma iron via transient generation of apotransferrin

Cardiosiderosis is a leading cause of mortality in transfusion-dependent thalassemias. Plasma non-transferrin-bound iron and its redox-active component, labile plasma iron, are key sources of iron loading in cardiosiderosis. Risk factors were identified in 73 patients with or without cardiosiderosis. Soluble transferrin receptor-1 levels were significantly lower in patients with cardiosiderosis (odds ratio 21). This risk increased when transfusion-iron loading rates exceeded the erythroid transferrin uptake rate (derived from soluble transferrin receptor-1) by >0.21 mg/kg/day (odds ratio 48). Labile plasma iron was >3-fold higher when this uptake rate threshold was exceeded, but non-transferrin-bound iron and transferrin saturation were comparable. The risk of cardiosiderosis was decreased in patients with low liver iron, ferritin and labile plasma iron, or high bilirubin, reticulocyte counts or hepcidin. We hypothesized that high erythroid transferrin uptake rate decreases cardiosiderosis through increased erythroid re-generation of apotransferrin. To test this, iron uptake and intracellular reactive oxygen species were examined in HL-1 cardiomyocytes under conditions modeling transferrin effects on non-transferrin-bound iron speciation with ferric citrate. Intracellular iron and reactive oxygen species increased with ferric citrate concentrations especially when iron-to-citrate ratios exceeded 1:100, i.e. conditions favoring kinetically labile monoferric rather than oligomer species. Excess iron-binding equivalents of apotransferrin inhibited iron uptake and decreased both intracellular reactive oxygen species and labile plasma iron under conditions favoring monoferric species. In conclusion, high transferrin iron utilization, relative to the transfusion-iron load rate, decreases the risk of cardiosiderosis. A putative mechanism is the transient re-generation of apotransferrin by an active erythron, rapidly binding labile plasma iron-detectable ferric monocitrate species.

A multiplex immunoassay method for simultaneous quantification of iron, vitamin A and inflammation status markers

Deficiencies of vitamin A and iron affect a significant portion of the world's population, and efforts to characterize patterns of these deficiencies are hampered by a lack of measurement tools appropriate for large-scale population-based surveys. Vitamin A and iron are not easily measured directly, so reliable proxy markers for deficiency status have been identified and adopted. Measurement of inflammatory markers is necessary to interpret vitamin A and iron status markers, because circulating levels are altered by inflammation. We developed a multiplex immunoassay method for simultaneous measurement of five markers relevant to assessing inflammation, vitamin A and iron status: α-1-acid glycoprotein, C-reactive protein, retinol binding protein 4, ferritin and soluble transferrin receptor. Serum and plasma specimens were used to optimize the assay protocol. To evaluate assay performance, plasma from 72 volunteers was assayed using the multiplex technique and compared to conventional immunoassay methods for each of the five markers. Results of the new and conventional assay methods were highly correlated (Pearson Correlations of 0.606 to 0.991, p<.0001). Inter-assay imprecision for the multiplex panel varied from 1% to 8%, and all samples fell within the limits of quantification for all assays at a single dilution. Absolute values given by the multiplex and conventional assays differed, indicating a need for further work to devise a new standard curve. This multiplexed micronutrient immunoassay technique has excellent potential as a cost effective tool for use in large-scale deficiency assessment efforts.

Soluble transferrin receptor in urine, a new biomarker for IgA nephropathy and Henoch-Schönlein purpura nephritis

OBJECTIVES

IgA nephropathy (IgAN) and Henoch-Schönlein purpura nephritis (HSPN) might represent different ends of a continuous spectrum of glomerular disease. In both conditions, upregulated soluble transferrin receptor (sTfR) might be excreted in urine, which could be a potential biomarker to monitor disease activity and therapeutic response.

METHODS

In this pilot study, 132 Caucasian patients consulting the Nephrology Department at the Ghent University Hospital because of a glomerulopathy and 50 normal controls were included. Urinary sTfR concentrations were determined in concentrated urine using a newly developed latex-enhanced immunonephelometric assay.

RESULTS

Median urinary sTfR concentration was higher in patients with a primary glomerulopathy than in healthy subjects (p<0.0001). More importantly, absolute median levels of urinary sTfR were markedly higher in patients with active IgAN or HSPN [10μg/L, 95% confidence interval (CI): 6-18μg/L] in comparison with those with other morphological types of glomerulopathy (2μg/L, 95%CI: 1-4μg/L) (p<0.0001). A statistically significant difference in urinary sTfR concentration was observed between patients with active IgAN or HSPN and patients who had achieved partial or complete remission (p<0.0001). Multiple regression analysis with urinary sTfR as dependent variable revealed that proteinuria was the main predictor of urinary sTfR concentration (r(2)=0.52, p<0.001).

CONCLUSION

Determination of sTfR in urine is a new and sensitive method for a potential biomarker of IgAN and HSPN.

Soluble transferrin receptor-1 levels in mice do not affect iron absorption

Soluble transferrin receptor-1 (sTfR1) concentrations are increased in the plasma under two conditions that are associated with increased iron absorption, i.e. iron deficiency and increased erythropoiesis. To determine the possible role of sTfR1 as a signaling mechanism for iron absorption, a hydrodynamic gene transfer technique was established to express transfected plasmid constructs of human sTfR1 (hsTfR1) and murine sTfR1 (msTfR1) from the livers of C57BL/6 mice. Iron absorption, serum iron levels and hepcidin expression were then measured. The hydrodynamic gene transfer technique proved to be an effective approach to achieving sustained expression of sTfR1 in mice. Although expression of high levels of sTfR1 significantly increased serum iron levels, repeated experiments showed that neither hsTfR1 nor msTfR1 had any effect on iron absorption or hepcidin mRNA expression levels. Thus, despite its attractiveness as a potential modifier of iron absorption, sTfR1 levels do not exert a regulatory effect on iron absorption.

Evaluation of an automated soluble transferrin receptor (sTfR) assay on the Roche Hitachi analyzer and its comparison to two ELISA assays

BACKGROUND

Soluble transferrin receptor (sTfR) assays are currently not standardized. This hinders data comparison between studies and also affects the use of a recently proposed model to estimate body iron.

METHODS

We evaluated the analytical performance of a fully automated sTfR immunoturbidimetric assay (Roche Diagnostics) and compared it with two ELISA assays (Ramco Laboratories and an in-house ELISA assay used in the body iron model).

RESULTS

The Roche assay showed excellent intra- and inter-assay precision (CV<5%). Prolonged exposure of serum samples to room temperature and multiple freeze-thaw cycles did not affect sTfR concentrations. Receiver-operator characteristic curve analysis demonstrated that the Roche assay (area-under-the-curve (AUC)=0.882) was superior to the Ramco assay (AUC=0.794) in predicting iron deficiency (defined as serum ferritin <10 microg/L; P=0.013). Method comparison between the Roche and the two ELISA assays showed good correlations (r>0.8); however, sTfR values by the Roche assay were on average 30% lower than values obtained with the two ELISA assays.

CONCLUSIONS

sTfR data measured with an immunoturbidimetric assay can be compared to a commonly used ELISA assay, and can be used in the body iron model through regression equations obtained in the present study.

Immunological study of complex formation between soluble transferrin receptor and transferrin

Transferrin receptor (TfR) is a dimeric transmembrane protein that provides iron transport from plasma to cells by binding and internalization of iron-loaded transferrin (Tf). Soluble transferrin receptor (sTfR) is an extracellular part of the TfR molecule that is truncated from the cell surface and released into the blood stream. Using monoclonal antibodies (HyTest Ltd., Turku, Finland), immunofluorescent methods for sTfR and sTfR-Tf complex determination were developed. Soluble TfR was isolated from human plasma, and complex formation between sTfR and Tf was studied by stepwise complex construction and by FPLC gel filtration. It was found that sTfR could bind two Tf molecules step by step when the sTfR-Tf complex is constructed in the plate wells. FPLC gel filtration of sTfR-Tf mixtures and analysis of sTfR and sTfR-Tf immunological activities in collected fractions showed that sTfR can form different complexes with TF depending upon the ratios between them: a 291-kDa compound is assumed to be a 2:1 sTfR/Tf complex, and a 345-kDa compound is assumed to be a 2:2 sTfR/Tf complex. Isolated sTfR eluted as a 237-kDa protein. FPLC gel filtration of serum revealed that all sTfR in serum is bound to Tf in a 2:2 complex, and no isolated sTfR can be found in serum. This raises the question as to the nature of the bonds that hold two molecules of sTfR together to form a dimer.

Evaluation of immunoassays for the measurement of soluble transferrin receptor as an indirect biomarker of recombinant human erythropoietin misuse in sport

Soluble transferrin receptor (sTfR) has been proposed as an indirect biomarker of the misuse of recombinant human erythropoietin in sport. An extended validation of four commercially available immunoassays for its measurement in serum is presented. Two ELISA techniques (ELISA1: Orion Diagnostica; ELISA2: R&D Systems), an immunoturbidimetric technique (Turbid: Roche Diagnostics), and a nephelometric technique (Nephel: Dade Behring) were investigated. Intra-laboratory precision better than 3% and correct accuracies were obtained for the Turbid and Nephel techniques using autoanalysers. Slightly worse precision (but always better than 11%) and correct accuracies were also obtained in almost all cases for the two ELISA techniques. Inter-laboratory results showed higher concordances for the ELISA procedures (intraclass correlation coefficients of 0.848 for ELISA1 and 0.973 for ELISA2 which was clearly better). Inter-technique correlations were good for the four techniques with lower dispersions found for the techniques using autoanalysers, i.e. Turbid and Nephel. While Turbid and ELISA1 results (expressed in mg/l) were comparable, results obtained with Nephel were approximately 2.7 times lower. The relationship between those three techniques was maintained when compared with ELISA2, which uses different units (nmol/l). We conclude that ELISA2 and Nephel in our hands were the most suitable techniques in terms of sensitivity, precision and accuracy, and adequacy of the calibration curve for the measurement of sTfR in real serum samples. Discrepancies observed in the results obtained with the different sTfR techniques showed that different reference standards were used and harmonization is recommended in order to obtain comparable results.

Multicenter evaluation of a fully mechanized soluble transferrin receptor assay on the Hitachi and cobas integra analyzers. the determination of reference ranges

Soluble transferrin receptor (sTfR) is reported to be a reliable marker for the diagnosis of iron deficiency, especially when iron metabolism is influenced by inflammatory disorders such as infection, chronic inflammation and cancer-related anemia. In the present multicenter study the analytical performance of a recently introduced, latex-enhanced immunoturbidimetric assay for the determination of soluble transferrin receptor (Tina quant [a] sTfR, Roche Diagnostics) on different fully mechanized analyzers such as Hitachi 917 and 911, and Cobas Integra 400 and 700 was evaluated. Within-run and between-run imprecision showed good results (CV<5% and <7%, respectively). The assay was found to be linear over a wide measuring range (0.4-35 mg/l). Endogenous substances did not interfere with the test results. Comparison of serum sTfR concentrations with those of heparinized plasma revealed good correlation (r>0.976). Method comparison with an existing fully mechanized method as well as with ELISA tests for sTfR showed very good correlation (r>0.987). Because of the lack of international standardization the results differed from each other up to 2.5-fold. The 95% of serum levels in healthy individuals ranged from 1.9 to 4.4 mg/l (n=427). However, the reference ranges should be reported in a sex-dependent manner, as 2.2-5.0 mg/l for men (n=211) and as 1.9-4.4 mg/l for premenopausal (n=216) and postmenopausal (n=45) women. The Tina quant [a] sTfR assay enables the precise, accurate, rapid and convenient determination of sTfR concentrations for routine clinical chemistry purposes.

Evaluation of iron status in anemic patients with rheumatoid arthritis using an automated immunoturbidimetric assay for transferrin receptor

We have evaluated a newly introduced immunoturbidimetric transferrin receptor assay (IdeA TfR-IT, Orion Diagnostica, Finland) in healthy subjects and in a study population consisting of patients with rheumatoid arthritis and juvenile chronic arthritis. The IdeA TfR-IT assay was found to provide reproducible results which were in good agreement with the ELISA assays from Orion Diagnostica (IDeA-ELISA, correlation R2=0.8, n=102) and R&D systems (Quantikine TfR ELISA assay, correlation R2=0.95, n=39). The analysis of the patient samples suggested that, on the basis of serum transferrin receptor and ferritin concentrations, in approximately one third of patients with rheumatoid arthritis anemia is due to the depletion of iron stores. Apparently, in all patients with rheumatoid arthritis iron deficiency must be considered as a potential cause of the anemia. Now, that assays which are suitable for automated analyzers have become available for the measurement of serum transferrin receptor, this analyte has the potential to become a part of the routine evaluation of iron status.

Laboratory screening for erythropoietin abuse in sport: an emerging challenge

The growing diffusion of banned practice to improve the athletic performances is forcing clinical laboratories to identify and standardize reliable assays to detect potential unfairness. Among the doping practices, the use of recombinant human erythropoietin is becoming fairly popular, due to simplicity and safeties of administration and troublesome detection. The heterogeneous response rate, the presence of a little but significant amount of naturally occurring hormone, the short half-life exhibited by recombinant human erythropoietin and the lack of standardization of commercial assays appear the main problems to overcome. Aim of the present article is to provide a critical review of some of the more widespread laboratory techniques currently available for the screening for erythropoietin abuse in sport.

Transferrin receptor on peripheral blood lymphocytes in iron deficiency anaemia

The effect of iron deficiency anaemia (IDA) on CD71 expression by peripheral blood lymphocytes was studied in 43 children with iron deficiency anaemia. 18 healthy age-matched children were selected as the control group. 11 children with beta-thalassaemia trait were also studied. Lymphocytes bearing CD71 were enumerated by flow cytometric analysis of peripheral blood. At diagnosis, CD71+ peripheral lymphocytes (mean+/-SE) was 5.90+/-0-76% in patients with IDA and 12.60+/-0.98% in healthy controls (P=0.000). In beta-thalassaemia trait patients the peripheral blood CD71+ lymphocytes were 7.80+/-1.20%. In IDA patients there was a statistically significant correlation between the levels of CD71+ peripheral lymphocytes and haemoglobin value (P = 0.000). In 19 patients studied at days 0 and 30 of oral iron therapy, the number of peripheral blood CD71+ lymphocytes was shown to be increased from 5.90+/-0.76% to 12.11+/-1.21%. In severe IDA presence of a limited number of CD71+ peripheral blood lymphocytes indicated that severe IDA should be borne in mind when considering conditions responsible for the suppression of lymphocyte proliferation.

Erythropoietin and iron

Serum ferritin concentration is most informative in estimating the amount of storage iron available for a particular individual. The serum transferrin receptor concentration, in contrast to serum ferritin, provides direct information about any deficit in the adequacy of iron supply to the erythropoiesis. The combination of serum transferrin receptor and serum ferritin provides complete information about storage and functional iron compartments. Using this combination along with the hemoglobin concentration, it is possible to define the iron nutritional status completely. Inflammatory conditions as well as parenteral iron administration interfere, however, with the direct and quantitative ferritin to storage iron relationship and, therefore, have to be considered carefully with respect to diagnostic purposes. The diagnostic use of the serum transferrin receptor is presently limited because of limitations in methodology and definition (standardization) of reference ranges.