Evaluation of an ELISA test for determination of the serum transferrin receptor. Demonstration of discordance between results obtained with two methods

Iron Deficiency and Iron Deficiency Anemia in Women with and without Obesity: NHANES 2001-2006

Obesity has been linked to numerous health and nutritional problems, including impaired iron metabolism, a common cause of anemia. We aimed to determine the prevalence of anemia, iron deficiency (ID), and iron deficiency anemia (IDA) among women aged 20-49 years based on body mass index (BMI) status. We used measures of iron status and body mass index from the 2001-2006 National Health and Nutrition Examination Survey (NHANES). Mean serum ferritin, erythrocyte protoporphyrin, and soluble transferrin receptor were higher, while those of serum iron, percent transferrin saturation, and mean cell volume (MCV) were lower in women with obesity than those with normal weight (all p < 0.016). ID based on the ferritin model was 12.5 ± 1.0% vs. 22.9 ± 1.6% (p < 0.001); 9.0 ± 0.9% vs. 20.0 ± 1.3% (p < 0.001) based on the MCV model; and 8.1 ± 1.0% vs. 10.5 ± 1.2% (p > 0.05) based on the BII model for women with normal weight and women with obesity, respectively. Anemia prevalence was 5.5 ± 0.8% (normal) vs. 9.3 ± 1.0% (obese) (p = 0.005). The IDA estimates based on the ferritin and MCV models were similar but higher than that from the BII model (p < 0.001). Generally, the prevalence rates of ID and anemia (and IDA) were higher for women with obesity, but the method used to define deficiency mattered. The choice of iron indices is important for estimating ID and IDA in populations with obesity.

Iron-containing micronutrient supplementation of Chinese women with no or mild anemia during pregnancy improved iron status but did not affect perinatal anemia

Universal prenatal daily iron-folic acid (IFA) and multiple micronutrient (MM) supplements are recommended to reduce the risk of low birth weight, maternal anemia, and iron deficiency (ID) during pregnancy, but the evidence of their effect on iron status among women with mild or no anemia is limited. The aim of this study was to describe the iron status [serum ferritin (SF), serum soluble transferrin receptor (sTfR), and body iron (BI)] before and after micronutrient supplementation during pregnancy. We examined 834 pregnant women with hemoglobin > 100 g/L at enrollment before 20 wk of gestation and with iron measurement data from a subset of a randomized, double-blind trial in China. Women were randomly assigned to take daily 400 μg of folic acid (FA) (control), FA plus 30 mg of iron, or FA, iron, plus 13 additional MMs provided before 20 wk of gestation to delivery. Venous blood was collected in this subset during study enrollment (before 20 wk of gestation) and 28-32 wk of gestation. We found that, at 28-32 wk of gestation, compared with the FA group, both the IFA and MM groups had significantly lower prevalence of ID regardless of which indicator (SF, sTfR, or BI) was used for defining ID. The prevalence of ID at 28-32 wk of gestation for IFA, MM, and FA were 35.3%, 42.7%, and 59.6% by using low SF, 53.6%, 59.9%, and 69.9% by using high sTfR, and 34.5%, 41.2%, and 59.6% by using low BI, respectively. However, there was no difference in anemia prevalence (hemoglobin < 110 g/L) between FA and IFA or MM groups. We concluded that, compared with FA alone, prenatal IFA and MM supplements provided to women with no or mild anemia improved iron status later during pregnancy but did not affect perinatal anemia. This trial was registered at clinicaltrials.gov as NCT00137744.

Serum soluble transferrin receptor concentrations in US preschool children and non-pregnant women of childbearing age from the National Health and Nutrition Examination Survey 2003-2010

BACKGROUND

Serum soluble transferrin receptor (sTfR) is recommended as a sensitive and accurate measure of iron deficiency (ID) in populations when only a single indicator can be used. The lack of assay standardization and of representative data on the distribution of sTfR in at-risk populations currently limits its utility.

METHODS

Using data from NHANES 2003-2010, we examined the distribution of sTfR and developed assay-specific cutoff values for defining elevated sTfR in 2 US populations groups: children aged 1-5 y (n=2820) and non-pregnant women aged 15-49 y (n=6575).

RESULTS

On average, children had higher geometric mean sTfR concentrations (4.09 mg/l; 95% CI: 4.04-4.14) than non-pregnant women (3.31 mg/l; 95% CI: 3.26-3.35) (p<0.001). Among children, those aged 1-2 y (compared to those aged 3-5 y), boys (compared to girls), and non-Hispanic black (NHB) children (compared to non-Hispanic white (NHW) and Mexican-American (MA) children) had higher sTfR concentrations. Among non-pregnant women, adolescents (15-19 y) had higher sTfR concentrations than adults aged 20-34 y but not compared to adults aged 35-49 y; NHB women (compared to NHW and MA women) and multiparous women (compared to nulliparous women) had higher sTfR concentrations. The derived cutoff values (97.5th percentile in a defined healthy reference population) for defining elevated sTfR in the US were 6.00 mg/l for children 1-5 y and 5.33 mg/l for non-pregnant women 15-49 y.

CONCLUSIONS

A different sTfR cutoff value may be needed in children and non-pregnant women to define ID.

Assessment of iron status in US pregnant women from the National Health and Nutrition Examination Survey (NHANES), 1999-2006

BACKGROUND

Total body iron calculated from serum ferritin and soluble transferrin receptor concentrations allows for the evaluation of the full range of iron status.

OBJECTIVE

We described the distribution of total body iron and the prevalence of iron deficiency (ID) on the basis of total body iron in US pregnant women.

DESIGN

We examined data from the National Health and Nutrition Examination Survey (NHANES) in 1999-2006 for 1171 pregnant women.

RESULTS

ID prevalence (±SE) in US pregnant women, which was defined as total body iron <0 mg/kg, was 18.0 ± 1.4%. Pregnant women in the first trimester had a higher mean total body iron than did pregnant women in the second or third trimesters. ID prevalence in pregnant women increased significantly with each trimester (6.9 ± 2.2%, 14.3 ± 2.1%, and 29.5 ± 2.7% in the first, second, and third trimesters, respectively). Pregnant women with parity ≥2 had the lowest mean total body iron and the highest prevalence of ID compared with values for pregnant women with parity of 0 or 1. The ID prevalence in non-Hispanic white pregnant women was significantly lower than in Mexican American or non-Hispanic black pregnant women. The mean total body iron and the prevalence of ID did not differ by educational level or by family income.

CONCLUSIONS

To our knowledge, these are the first data on total body iron distributions for a representative sample of US pregnant women. Low total body iron is more prevalent in pregnant women in the second or third trimesters, in Mexican American pregnant women, in non-Hispanic black pregnant women, and in women with parity ≥2.

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.

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.

Serum transferrin receptor in the evaluation of the iron status in elderly hospitalized patients with anemia

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.