Serum transferrin receptors: Distribution and diagnostic performance in pre-school children

Reference intervals and percentiles for soluble transferrin receptor and sTfR/log ferritin index in healthy children and adolescents

OBJECTIVES

Soluble transferrin receptor (sTfR) is a marker of both erythropoiesis and iron status and is considered useful for detecting iron deficiency, especially in inflammatory conditions, but reference intervals covering the entire pediatric age spectrum are lacking.

METHODS

We studied 1,064 (48.5 % female) healthy children of the entire pediatric age spectrum to determine reference values and percentiles for sTfR and the ratio of sTfR to log-ferritin (sTfR-F index) using a standard immunoturbidimetric assay.

RESULTS

Soluble TfR levels were highly age-specific, with a peak in infancy and a decline in adulthood, whereas the sTfR-F index was a rather constant parameter. There were positive linear relationships for sTfR with hemoglobin (Hb) (p=0.008) and transferrin (females p<0.001; males p=0.003). A negative association was observed between sTfR and ferritin in females (p<0.0001) and for transferrin saturation and mean corpuscular volume (MCV) in both sexes (both p<0.0001). We found a positive relationship between sTfR and body height, body mass index (BMI) and inflammatory markers (CrP p<0.0001; WBC p=0.0172), while sTfR-F index was not affected by inflammation.

CONCLUSIONS

Soluble TfR values appear to reflect the activity of infant erythropoiesis and to be modulated by inflammation and iron deficiency even in a healthy cohort.

[Biological diagnosis of iron deficiency in children]

Measurement of serum ferritin (SF) is currently the laboratory test recommended for diagnosing iron deficiency. In the absence of an associated disease, a low SF value is an early and highly specific indicator of iron deficiency. The WHO criteria proposed to define depleted storage iron are 12μg/L for children under 5 years and 15μg/L for those over 5 years. A higher threshold of 30μg/L is used in the presence of infection or inflammation. Iron deficiency anemia, with typical low mean corpuscular volume and mean corpuscular hemoglobin, is only present at the end stage of iron deficiency. Other diagnostic tests for iron deficiency including iron parameters (low serum iron, increased total iron-binding capacity, low transferrin saturation) and erythrocyte traits (low mean corpuscular volume, increased zinc protoporphyrin) provide little additional diagnostic value over SF. In children, serum soluble transferrin receptor (sTfR) has been reported to be a sensitive indicator of iron deficiency and is relatively unaffected by inflammation. On the other hand, sTfR is directly related to extent of erythroid activity and not commonly used in clinical practice. In population surveys, approaches based on combinations of markers have been explored to improve the specificity and sensitivity of diagnostic. In addition to Hb value determination, a combination of parameters (among transferrin saturation, zinc protoporphyrin, mean corpuscular volume or serum ferritin) was generally used to assess iron deficiency. More recently sTfR/ ferritin index were evaluated, sTfR in conjunction with SF allowing to better distinguishing iron deficiency from inflammatory anemia. Also, hepcidin measurements appeared an interesting marker for diagnosing iron deficiency and identifying individuals in need of iron supplementation in populations where inflammatory or infectious diseases are frequently encountered. Reticulocyte Hb content (CHr) determination is an early parameter of iron deficiency erythropoiesis. CHr can be measured with several automated hematology analyzers and so, used for individual's iron status assessment. In addition to Hb concentration determination, individual's iron status is commonly assessed in the pediatric clinical practice by the SF measurement accompanied by the determination of C-reactive protein for detection of a simultaneous acute infection and/or inflammation.

Prevalence of Inherited Hemoglobin Disorders and Relationships with Anemia and Micronutrient Status among Children in Yaoundé and Douala, Cameroon

Information on the etiology of anemia is necessary to design effective anemia control programs. Our objective was to measure the prevalence of inherited hemoglobin disorders (IHD) in a representative sample of children in urban Cameroon, and examine the relationships between IHD and anemia. In a cluster survey of children 12-59 months of age (n = 291) in Yaoundé and Douala, we assessed hemoglobin (Hb), malaria infection, and plasma indicators of inflammation and micronutrient status. Hb S was detected by HPLC, and α⁺thalassemia (3.7 kb deletions) by PCR. Anemia (Hb < 110 g/L), inflammation, and malaria were present in 45%, 46%, and 8% of children. A total of 13.7% of children had HbAS, 1.6% had HbSS, and 30.6% and 3.1% had heterozygous and homozygous α⁺thalassemia. The prevalence of anemia was greater among HbAS compared to HbAA children (60.3 vs. 42.0%, p = 0.038), although mean Hb concentrations did not differ, p = 0.38). Hb and anemia prevalence did not differ among children with or without single gene deletion α⁺thalassemia. In multi-variable models, anemia was independently predicted by HbAS, HbSS, malaria, iron deficiency (ID; inflammation-adjusted ferritin <12 µg/L), higher C-reactive protein, lower plasma folate, and younger age. Elevated soluble transferrin receptor concentration (>8.3 mg/L) was associated with younger age, malaria, greater mean reticulocyte counts, inflammation, HbSS genotype, and ID. IHD are prevalent but contribute modestly to anemia among children in urban Cameroon.

Reference Values of Reticulocyte Hemoglobin Content and Their Relation With Other Indicators of Iron Status in Healthy Children

Reticulocyte hemoglobin content (CHr) is considered an indicator of functional iron deficiency, but is understudied in children. The goals of this study are to determine the reference intervals for CHr in healthy children, and their relation with iron parameters, erythropoiesis, and individual conditions. A total of 902 children without iron deficiency, aged 1 to 11 years were analyzed in a cross-sectional study. Besides a physical examination of the subjects and a questionnaire completed by their parents, the complete blood count, serum transferrin receptor, ferritin, transferrin saturation, erythrocyte protoporphyrin, serum erythropoietin, C-reactive protein, and CHr levels were measured. Changes in CHr, iron status, and erythropoiesis at different age intervals were analyzed and linear multiple regression was used to identify the factors that determine CHr variability. Mean value obtained for CHr was 30.9±1.8 pg (P2.5-P97.5: 26.9 to 34.3 pg), but the influence of age on CHr (the values increased with age) and on the iron parameters justified the establishment of different reference ranges. In addition to age, nutritional status, hematologic measurements, reticulocytes, transferrin saturation, and erythrocyte protoporphyrin accounted for 39% of CHr variability.

Using Soluble Transferrin Receptor and Taking Inflammation into Account When Defining Serum Ferritin Cutoffs Improved the Diagnosis of Iron Deficiency in a Group of Canadian Preschool Inuit Children from Nunavik

The prevalence of iron depletion, iron deficient erythropoiesis (IDE), and iron deficiency anemia (IDA) was assessed in preschool Inuit children using soluble transferrin receptor (sTfR) and traditional indicators of iron status while disregarding or taking inflammation into account when defining SF cutoffs. Iron depletion was defined as follows: (1) SF < 15 μg/L regardless of the C-reactive protein (CRP) level and (2) SF < 15 or <50 μg/L with CRP ≤ 5 or >5 mg/L, respectively. IDE corresponded to iron depletion combined with total iron binding capacity > 72 μmol/L and/or transferrin saturation < 16%. Iron depletion and IDE affected almost half of the children when accounting for inflammation, compared to one-third when the SF cutoff was defined regardless of CRP level (P < 0.0001). The prevalence of IDE adjusted for inflammation (45.1%) was very similar to the prevalence observed when sTfR was used as a sole marker of IDE (47.4%). The prevalence of anemia was 15%. The prevalence of IDA (IDE + hemoglobin < 110 g/L) was higher when accounting for than when disregarding inflammation (8.0% versus 6.2%, P = 0.083). Using sTfR and different SF cutoffs for children with versus without inflammation improved the diagnosis of iron depletion and IDE. Our results confirm that Inuit children are at particularly high risk for iron deficiency.

Reference values of serum transferrin receptor (sTfR) and sTfR/log ferritin index in healthy children

ABSTARCT The aims of this study were to determine appropriate reference ranges for serum transferrin receptor (sTfR) and sTfR/log ferritin (sTfR-F index) in healthy children and their relationship with iron parameters, erythropoiesis, and other conditions presented by the subject. A total of 902 children with normal iron status, aged 1-11 years, were included in a cross-sectional study. A physical examination was conducted and z-score of body mass index (zBMI) obtained. Complete blood count, iron biomarkers, erythropoietin, C-reactive protein, sTfR, and sTfR/log ferritin were determined. Linear multiple regression was applied to identify the factors that determined sTfR and sTfR-F index variability. Mean values for sTfR and sTfR-F index were 1.22 ± 0.28 mg/L (95% confidence interval [CI]: 1.2-1.23) and 0.87 ± 0.25 (95% CI: 0.85-0.88). The reference intervals (2.5th to 97.5th percentiles [P2.5-P97.5]) were 0.78-1.9 mg/L and 0.49-1.46, respectively. sTfR and sTfR-F values decreased with age (P <.03 and P <.0001, respectively). No changes were observed with sex. Changes in sTfR and sTfR-F index were consistent with ferritin and erythropoietin variations. Iron biomarkers, erythropoietin, and zBMI predicted 19% and 18.1% of the sTfR and sTfR-F index variability. The results provide reference ranges for sTfR and sTfR-F index in healthy children for clinical use in the assessment of body iron status. Both biomarkers are predicted by iron parameters, erythropoietin, and zBMI.

Relationship Between being Overweight and Iron Deficiency in Adolescents

OBJECTIVE

Being overweight has been considered to be a risk factor of iron deficiency (ID). The objective of this study was to examine the relationship between being overweight and body iron status among Taiwanese adolescents.

METHODS

A total of 2099 adolescents (1327 female) aged 12-19 years from four middle schools and one college in southern Taiwan participated in this study. Data on sex, age, body weight, height, hemoglobin concentration, plasma ferritin (PF), and serum iron (SI) levels were collected. According to the age- and sex-specific body mass index (BMI) percentiles, the participants were divided into four weight groups: underweight (<5(th) percentile), normal weight (5-84(th) percentile), overweight (85-94(th) percentile), and obese (≥95(th) percentile). A multivariate logistic regression model was used to estimate the odds ratio (OR) and the 95% confidence interval (CI) for each factor.

RESULTS

The correlation coefficients of linear regression were positive for BMI-hemoglobin and BMI-PF, but negative for BMI-SI. Compared with the normal-weight group, the obese group had a lower risk of PF level <15 μg/L with an OR (95% CI) of 0.51 (0.30-0.87) but a higher risk of SI <60 μg/dL with an OR (95% CI) of 1.78 (1.34-2.37). The percentages of low PF declined as BMI increased, but the percentages of low SI rose, from underweight to obesity groups.

CONCLUSION

The relationship between being overweight and depleted iron store depends on which indicator is used to define the iron deficiency. Being overweight or obese would not be a risk factor of ID in adolescents, if ID were defined by PF rather than SI level.

Increased whole blood manganese concentrations observed in children with iron deficiency anaemia

A prospective observational study was carried out at Alder Hey Children's Hospital, Liverpool, England, UK on children aged 1-6 years attending the pathology department for routine blood tests (n=225). Whole blood manganese concentrations were measured plus the following markers of iron status; haemoglobin, MCV, MCH, RBC count, ferritin, transferrin saturation and soluble transferrin receptors. Multiple regression analysis was performed, with blood manganese as the dependent variable and factors of iron status, age and gender as independent variables. A strong relationship between blood manganese and iron deficiency was demonstrated (adjusted R(2)=34.3%, p<0.001) and the primary contributing factors to this relationship were haematological indices and soluble transferrin receptors. Subjects were categorised according to iron status using serum ferritin, transferrin saturation and haemoglobin indices. Children with iron deficiency anaemia had higher median blood manganese concentrations (16.4 μg/L, range 11.7-42.4, n=20) than children with iron sufficiency (11 μg/L, range 5.9-20.9, n=59, p<0.001). This suggests that children with iron deficiency anaemia may be at risk from manganese toxicity (whole blood manganese >20 μg/L), and that this may lead to neurological problems. Treatment of iron deficiency in children is important both to improve iron status and to reduce the risk of manganese toxicity.

The significance of serum transferrin receptor levels in the diagnosis of the coexistence of anemia of chronic disease and iron deficiency anemia

OBJECTIVE

Iron deficiency anemia is the most common cause of microcytic anemia throughout the world. Ferritin levels are good indicators of iron stores; however, levels may increase irrespective of iron stores in cases of chronic disease. Therefore, it is difficult to diagnose iron deficiency anemia coexisting with anemia of chronic disease.

MATERIALS AND METHODS

To determine the level of transferrin receptor in subjects, 30 patients with iron deficiency anemia, 30 patients with anemia of chronic disease and 30 patients with both diseases were included in the study.

RESULTS

Mean serum transferrin receptor levels were 5.99±2.98 mg/L in the iron deficiency anemia group, 1.90±1.15 mg/L in the anemia of chronic disease group and 3.07±0.90 mg/L in the combination group. Comparing groups with each other revealed significant differences (p<0.05).

CONCLUSION

It is concluded that the assessment of serum transferrin receptor levels is a useful method for the diagnosis of iron deficiency anemia in patients.

Age, beta thalassaemia trait, and iron-deficient anaemia significantly affect reticulocyte indices in pre-school children

BACKGROUND

Reticulocyte indices are easy to obtain, low cost parameters and have gained interest in the field of diagnosing anaemias of childhood.

METHODS

We assessed distribution, age and gender variation, relation to indices of iron metabolism and diagnostic performance of reticulocyte haemoglobin content (CHr), percentage of microcytic reticulocytes (micro_r), percentage of hypochromic reticulocytes (hypo_r), and percentage of reticulocytes with low CHr (low_CHr) in 386 pre-school children classified in four groups: healthy, iron deficiency (ID), iron deficiency anaemia (IDA), and beta-thalassaemia carriers (beta-thal).

RESULTS

Age had a positive effect in CHr (Spearman's rho = 0.21) and a negative effect in hypo_r (Spearman's rho = -0.2) in healthy children. CHr and low_CHr were related to ferritin in the IDA group (Spearman's rho 0.55 and -0.53, respectively). In the beta-thal group, HbA(2) is strongly related to all reticulocyte indices. micro_r and CHr performed best in discriminating between IDA and beta-thal heterozygosity (ROC analysis, area under the curve (AUC): 0.76 and 0.74, respectively). CHr achieved the best AUC (0.58) in identifying ID among children without anaemia.

CONCLUSION

Age, IDA and beta-thal significantly affect reticulocyte indices. CHr and micro_r may have a role as screening tools in discriminating between IDA and beta-thal heterozygosity.