Serum hepcidin as a diagnostic test of iron deficiency in premenopausal female blood donors

Background

Currently used indicators of iron status have limitations. Hepcidin, a key regulator of iron metabolism, is reduced in iron deficiency. We sought to determine the properties of hepcidin as a diagnostic test of iron deficiency.

Design and Methods

Sera from female, non-anemic, whole blood donors were analyzed for hepcidin (enzyme-linked immunosorbent assay), ferritin, soluble transferrin receptor and C-reactive protein. Iron deficiency was defined as (i) serum ferritin less than 15 ng/mL or (ii) soluble transferrin receptor /log(ferritin) index greater than 3.2 if the C-reactive protein concentration was less than 10 mg/L, or greater than 2.2 if the C-reactive protein concentration was greater than 10 mg/L). Receiver operating characteristic curves were plotted to determine the overall utility and identify optimal cut-points of hepcidin as a test of iron deficiency.

Results

In 261 blood donors the prevalence of iron deficiency defined by ferritin concentration was 59/261 [22.6% (17.5, 27.7)], whereas defined by soluble transferrin receptor/log(ferritin) index it was 53/261 [20.4% (15.4, 25.2)]. The 95% reference range of hepcidin concentration in the iron-replete population was 8.2–199.7 ng/mL. The area under the receiver operating characteristic curve for hepcidin compared with ferritin concentration less than 15 ng/mL was 0.87 (0.82, 0.92), while that compared with the soluble transferrin receptor /log(ferritin) index was 0.89 (95% CI 0.84, 0.93). For a diagnosis of iron deficiency defined by the soluble transferrin receptor/log(ferritin) index, hepcidin less than 8 ng/mL had a sensitivity of 41.5% and a specificity of 97.6%, while hepcidin less than 18 ng/mL had a sensitivity of 79.2% and a specificity of 85.6%.

Conclusions

Serum hepcidin concentration may be a useful indicator of deficient iron stores. Further studies are required to evaluate the role of hepcidin in the diagnosis of iron deficiency in other groups of patients.     

Serum ferritin levels in anemia of rheumatoid arthritis

Thirty-five anemic patients with rheumatoid arthritis were studied to determine the relationship between serum ferritin levels and body iron status, as assessed by the grading of bone marrow iron stores. The incidence of greatly reduced or absent marrow iron stores was 60%. Peripheral blood smear, RBC indices, serum iron, and iron binding capacity correlated poorly with stainable marrow iron. Serum ferritin levels only correlated approximately with iron stores, and in iron deficient rheumatoid patients the levels were higher than would be expected in patients with uncomplicated iron deficiency. The study shows that reduced marrow iron stores is common in patients with rheumatoid arthritis, and that the serum ferritin concentration may provide a useful indication of reduced body iron stores in these subjects, but only if a range of normal values can be established for this disease.     

The differentiation of anaemia in rheumatoid arthritis: parameters of iron-deficiency in an Indian rheumatoid arthritis population

Iron deficiency anaemia (IDA) is common in Indian patients with rheumatoid arthritis (RA). We evaluated red blood cell indices, serum iron related and bone marrow iron stores measurements in diagnosing iron deficiency in patients with RA. Fifty consecutive anaemic patients with RA had their complete blood counts, red cell indices, serum iron, serum ferritin and serum total iron binding capacity (TIBC) measured and underwent posterior iliac crest bone marrow aspiration. Fixed smears were stained for iron with Perl’s Prussian blue and patients who had no (grade 0) or minimal stainable iron (grade I) were regarded as iron deficient and rest iron replete (grade II–IV) and hence as having anaemia of chronic disease (ACD). To determine diagnostic power of tests used for diagnosing iron deficiency in addition to positive likelihood ratio, sensitivity, specificity and negative predictive values; receiver operating characteristics (ROC) curves were plotted and areas under the receiver-operating curves were compared. Eighteen patients (36%) had IDA and 32 (64%) had ACD. Correlation between the bone marrow iron stores and serum ferritin was poor in the IDA group (r = −0.09, P = 0.57) and significant in the ACD group (r = 0.79, P < 0.0001). Areas under the ROC curves for mean corpuscular haemoglobin (MCV), serum iron, TIBC and mean corpuscular haemoglobin concentration (MCHC) were relatively low (0.52, 0.71, 0.75 and 0.77, respectively) and these tests had low positive likelihood ratios (1.08, 2.13, 4.62 and 1.5, respectively). Both area under ROC curve [0.98, 95% confidence interval (0.94, 0.99)] and negative predictive value (97%) were highest when cut off serum ferritin was <82 μg/l. In patients with RA serum iron, TIBC, MCV and MCHC have limited value in diagnosing iron deficiency. In this study compared to American and European studies a much higher cut off value of serum ferritin had most diagnostic power for detecting iron deficiency. Bone marrow iron stores measurements appears to be the most reliable method for diagnosing IDA however, it needs to be taken in conjunction with other laboratory findings and the clinical scenario.     

Serum transferrin receptor: a quantitative measure of tissue iron deficiency

This study was undertaken to evaluate the role of serum transferrin receptor measurements in the assessment of iron status. Repeated phlebotomies were performed in 14 normal volunteer subjects to obtain varying degrees of iron deficiency. Serial measurements of serum iron, total iron-binding capacity, mean cell volume (MCV), free erythrocyte protoporphyrin (FEP), red cell mean index, serum ferritin, and serum transferrin receptor were performed throughout the phlebotomy program. There was no change in receptor levels during the phase of storage iron depletion. When the serum ferritin level reached subnormal values there was an increase in serum receptor levels, which continued throughout the phlebotomy program. Functional iron deficiency was defined as a reduction in body iron beyond the point of depleted iron stores. The serum receptor level was a more sensitive and reliable guide to the degree of functional iron deficiency than either the FEP or MCV. Our studies indicate that the serum receptor measurement is of particular value in identifying mild iron deficiency of recent onset. The iron status of a population can be fully assessed by using serum ferritin as a measure of iron stores, serum receptor as a measure of mild tissue iron deficiency, and hemoglobin concentration as a measure of advanced iron deficiency.     

Iron Stores in Blood Donors Evaluated by Serum Ferritin

Male and female blood donors were grouped according to their blood donations, and the iron stores were estimated by a two-site immunoradiometric assay for ferritin. Hb serum iron, serum transferrin and transferrin saturation were also measured. A remarkable low serum ferritin concentration was found in male donors, who had donated blood one or two times. This might indicate that the serum ferritin concentration in male blood donors is not linearly correlated to the iron stores. Among 30 female donors 14 had ferritin values below 10 ng/ml, which have been shown to be indicative of iron deficiency. The serum ferritin concentration could not be used to predict the donors who developed low Hb values by the blood donation which followed. Serum ferritin was correlated to serum iron in men and to serum transferrin and transferrin saturation in both men and women.     

Diagnosis of hemochromatosis in young subjects: predictive accuracy of biochemical screening tests

The reliability of serum iron, transferrin saturation, and serum ferritin in the detection of early iron overload in hemochromatosis was determined in 120 young (less than 35 yr old) relatives whose genetic susceptibility for the disease was determined by HLA typing of families. Serum ferritin and transferrin saturation demonstrated high levels of sensitivity and specificity, whereas serum iron concentration was an unreliable test in the detection of hemochromatosis. In hemochromatosis homozygotes there was an excellent correlation between serum ferritin and mobilized body iron (r = 0.92), 1 microgram/L of serum ferritin corresponding to approximately 7.5 mg of body iron stores. For a given age, serum ferritin values were higher in homozygotes compared with heterozygotes or homozygous-normal subjects and increased by approximately 65 micrograms/L X yr, reflecting the progressive accumulation of iron in hemochromatosis homozygotes. All hemochromatosis subjects with either hepatic fibrosis or cirrhosis had serum ferritin concentrations greater than 700 micrograms/L. We conclude that the combination of serum ferritin and transferrin saturation is a reliable screening regimen for the detection of hemochromatosis and for predicting the level of body iron stores in young hemochromatosis subjects.     

Value of serum ferritin as an index of iron deficiency in elderly anaemic patients

Serum ferritin was correlated with bone marrow iron stores in 35 elderly anaemic patients. All 19 patients with low serum ferritin had iron deficiency as assessed on bone marrow examination, whereas six patients with low or absent bone marrow iron stores had serum ferritin within normal range. A low serum ferritin invariably indicates iron deficiency and has a better correlation than low serum iron. Serum ferritin should be included in the initial investigation of the anaemic elderly.     

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.     

Diagnosis and management of iron-deficiency anaemia

Anaemia is typically the first clue to iron deficiency, but an isolated haemoglobin measurement has both low specificity and low sensitivity. The latter can be improved by including measures of iron-deficient erythropoiesis such as the transferrin iron saturation, mean corpuscular haemoglobin concentration, erythrocyte zinc protoporphyrin, percentage of hypochromic erythrocytes or reticulocyte haemoglobin concentration. However, the changes in these measurements with iron deficiency are indistinguishable from those seen in patients with the anaemia of chronic disease. The optimal diagnostic approach is to measure the serum ferritin as an index of iron stores and the serum transferrin receptor as a index of tissue iron deficiency. The treatment of iron deficiency should always be initiated with oral iron. When this fails because of large blood losses, iron malabsorption, or intolerance to oral iron, parenteral iron can be given using iron dextran, iron gluconate or iron sucrose.     

Inflammation and iron deficiency in the hypoferremia of obesity

CONTEXT: Obesity is associated with hypoferremia, but it is unclear if this condition is caused by insufficient iron stores or diminished iron availability related to inflammation-induced iron sequestration. OBJECTIVE: To examine the relationships between obesity, serum iron, measures of iron intake, iron stores and inflammation. We hypothesized that both inflammation-induced sequestration of iron and true iron deficiency were involved in the hypoferremia of obesity. DESIGN: Cross-sectional analysis of factors anticipated to affect serum iron. SETTING: Outpatient clinic visits. PATIENTS: Convenience sample of 234 obese and 172 non-obese adults. MAIN OUTCOME MEASURES: Relationships between serum iron, adiposity, and serum transferrin receptor, C-reactive protein, ferritin, and iron intake analyzed by analysis of covariance and multiple linear regression. RESULTS: Serum iron was lower (75.8+/-35.2 vs 86.5+/-34.2 g/dl, P=0.002), whereas transferrin receptor (22.6+/-7.1 vs 21.0+/-7.2 nmol/l, P=0.026), C-reactive protein (0.75+/-0.67 vs 0.34+/-0.67 mg/dl, P<0.0001) and ferritin (81.1+/-88.8 vs 57.6+/-88.7 microg/l, P=0.009) were higher in obese than non-obese subjects. Obese subjects had a higher prevalence of iron deficiency defined by serum iron (24.3%, confidence intervals (CI) 19.3-30.2 vs 15.7%, CI 11.0-21.9%, P=0.03) and transferrin receptor (26.9%, CI 21.6-33.0 vs 15.7%, CI 11.0-21.9%, P=0.0078) but not by ferritin (9.8%, CI 6.6-14.4 vs 9.3%, CI 5.7-14.7%, P=0.99). Transferrin receptor, ferritin and C-reactive protein contributed independently as predictors of serum iron. CONCLUSIONS: The hypoferremia of obesity appears to be explained both by true iron deficiency and by inflammatory-mediated functional iron deficiency.     

Assessment of iron stores in anemic geriatric patients

Of patients referred to a geriatric service, 66 were identified who were clearly anemic (hemoglobin less than 12 g in men, less than 11 g in women) but whose cause of anemia was not readily identifiable by noninvasive measures. The difficulty in distinguishing iron deficiency from chronic disease as a cause of anemia by noninvasive means (serum iron, total iron binding capacity, transferrin saturation ratio, and serum ferritin), is highlighted by the poor power of these investigations when compared with bone marrow iron stores. A transferrin saturation ratio of less than 11% and a serum ferritin of less than 45 pg/L serve better than currently accepted values to identify iron deficiency in this population.     

Clinical evaluation of iron deficiency

While the prevalence of iron deficiency has remained relatively constant, there has been continuing refinement in its laboratory recognition, especially with the recent introduction of serum ferritin and FEP measurements. It is helpful to classify iron deficiency into three stages. Storage iron depletion is identified by marrow examination or serum ferritin, iron deficient erythropoiesis by TS, FEP, or MCV, and iron deficiency anemia by hemoglobin concentration or therapeutic iron trial. Combinations of these measurements have been used in prevalence studies to obtain a quantitative measure of body iron stores. The optimal laboratory approach to diagnosing iron deficiency depends on the clinical setting. In the office or outpatient clinic, iron depletion is best recognized by the serum ferritin, although the TS, FEP, and MCV are helpful in gauging its severity. In hospitalized patients with overt anemia, the TS, FEP, and MCV are much less helpful because similar changes are seen in the anemia of chronic disease. Examination of marrow iron remains the method of choice, especially in patients with infection, chronic disease, malignancy, or liver disease, although in many clinical situations the same information can be obtained from a serum ferritin. Serial measurements of serum ferritin have been particularly useful in monitoring patients at high risk of iron deficiency such as those with rheumatoid arthritis, chronic inflammatory bowel disease, or chronic renal failure.     

Body iron stores in patients subjected to surgery of the large bowel

Iron stores as estimated by serum ferritin concentration were studied in 40 patients subjected to colon surgery in reference to postoperative complications and restoration of iron stores, as well as to dietary and supplementary iron. The results showed that empty iron stores are common in patients subjected to colon surgery; 40 percent of the patients had a total loss before the operation. Preoperatively empty iron stores were associated (P<.01) with an increased risk of postoperative complications that were not explained by other nutritional parameters. Surgery of the colon did not affect serum ferritin concentration or iron stores acutely or long-term. Intake of dietary iron was determined by food recording for seven days in all patients and was compared to 40 controls. The preoperative hemorrhagia and lower daily intake of dietary iron (8±3 mg) in the patients than in the controls (14±4 mg) may explain the empty iron stores. However, patients with normal iron stores also had low amounts of dietary iron (9±3 mg). In 12 patients with empty iron stores the effects of ferrous sulfate (80 mg Fe⁺⁺) three times daily for six weeks were studied. The patients responded well to the therapy. It is concluded that preoperatively empty iron stores are common in patients subjected to colon surgery, and that this raises the risk of postoperative complications. Colon operations are not followed by acute or long-term changes in serum ferritin concentration or iron stores. The restoration of iron is achieved by oral iron therapy.     

Red cell ferritin and iron stores in patients with chronic disease

Serum and red cell ferritin were determined in a heterogeneous group of 59 patients with chronic disease undergoing a bone marrow biopsy. There was very little correlation between serum and red cell ferritin (r = 0.53). Although serum ferritin increased in relation to increased bone marrow iron stores, only 1 out of 8 patients with absent marrow iron stores and none of 8 patients with reduced marrow iron stores had a decreased serum ferritin. In contrast, 6 of 8 patients with absent iron stores had a reduced red cell ferritin concentration. There was no significant difference between the mean red cell ferritin of the patients with reduced, normal and mild-moderately increased marrow iron stores (30, 26 and 34 ag/cell). Red cell ferritin was decreased in 78% of a group of 32 patients with a low mean cell volume. In the patients studied, red cell ferritin was a better indicator of absent iron stores than serum ferritin. However, red cell ferritin did not detect a reduction in the iron status until the marrow iron stores were completely depleted. Apparently, during normal erythropoiesis the primitive erythroblasts continue to take up iron irrespective of the amount of iron available in the stores.     

Duodenal ferritin content and structure: relationship with body iron stores in man

The relationship between serum ferritin and duodenal ferritin was examined in normal subjects and in patients with iron deficiency, secondary iron overload, or idiopathic hemochromatosis (IHC). A positive correlation between serum ferritin and duodenal ferritin concentrations was found in all groups. In the iron-overload conditions, duodenal ferritin concentration was lower at all levels of serum ferritin in comparison with normal and iron-deficient subjects. Patients with secondary iron overload did not differ from those with IHC, which indicates that any decrease in duodenal ferritin concentration was secondary to the excess body iron stores. Purified duodenal ferritin from normal subjects and patients with iron-overload conditions showed the same two distinct isoferritins by isoelectric focusing. After the oral administration of iron, two additional isoferritins were detected. These resembled the major isoferritins of liver.     

The Relationship between Maternal and Infant Iron Status

Serum ferritin, iron and haemoglobin (Hb) concentrations were determined in 103 pregnant women and in the cord of their normal full-term offspring. In 50 of the cases the placental non-haem iron was also measured. The correlations between serum ferritin concentration and other measurements of iron status were similar in both maternal and cord blood suggesting that cord serum ferritin concentration may, as in adults, reflect neonatal iron stores. The inverse relationship found between cord serum ferritin and Hb concentrations (r = –0.35, P < 0.001) suggests that the amount of iron in foetal stores is influenced by that required for Hb. When Hb levels are elevated, as was demonstrated in babies of older mothers, significantly lower serum ferritin were found. Thus a low cord serum ferritin concentration does not necessarily indicate that less iron was transferred to the foetus. Maternal iron reserve, as reflected by serum ferritin concentration, was shown to be related to the amount of non-haem iron in the placenta (r = 0.41, P < 0.005), but this iron does not seem to form part of foetal iron stores as it does not correlate with measurements of foetal iron status. A week correlation between cord and maternal serum ferritin concentrations was demonstrated (r = 0.21, P < 0.05) but its biological significance is questionable.     

Serum ferritin in evaluation of iron status in children

The value of serum ferritin in assessing iron status was studied in 192 preschool age children between the ages of 3 and 60 months. Children were considered to have iron deficiency if the transferrin saturation was less than 16% and the peripheral smear revealed microcytosis and hypochromia. Anemia was present when hemoglobin level was 10.5 g/dl. According to this criteria, 46% of children screened had either iron deficiency (11.5%) or iron deficiency anemia (34.4%). Mean serum ferritin for the iron deficiency anemia group was 39.1 ng/mg as compared to 41.7 ng/ml for the iron deficiency group and 84.7 ng/ml for the normal group. Even though the serum ferritin level was lower in the iron deficiency group, the difference in the means did not reach statistical significance. Furthermore, only 30% of children who had either iron deficiency or iron deficiency anemia had serum ferritin level of less than 12 ng/ml, the level considered diagnostic for iron deficiency. It can be concluded that serum ferritin cannot be used alone for iron status determination. Multiple parameters will make the assessment more reliable.     

Anaemia of rheumatoid arthritis: serum erythropoietin concentrations and red cell distribution width in relation to iron status.

Immunoreactive serum erythropoietin concentrations were measured in 35 patients with anaemia associated with active rheumatoid arthritis. Based on an evaluation of stainable iron in the bone marrow (marrow iron grade 0-4) and serum ferritin concentrations (concentrations less than or equal to 60 micrograms/l compatible with iron deficiency) the anaemia was found to be complicated by iron deficiency in 19/35 (54%) of the patients. The mean serum erythropoietin level (57.6 (SD) 27.3) U/l) was sufficiently raised for the degree of anaemia irrespective of the size of the marrow iron stores. Thus the data do not support the contention that suppressed secretion of erythropoietin is involved in the pathogenesis of anaemia of chronic disorders. There was a significant inverse correlation between the haemoglobin concentration and log serum erythropoietin in the patients with rheumatoid arthritis. In the patients with adequate iron stores, but not in the iron depleted patients, there was a tendency for serum erythropoietin concentrations to correlate positively both with C reactive protein and erythrocyte sedimentation rate. Red cell distribution width (mean (SD) 16.3 (1.8)%) was above normal (11.5-14.5%) both in the iron replete and the iron depleted patients, and the mean red cell distribution width values did not differ significantly among the two subpopulations. The plasma lactoferrin concentration (mean (SD) 137.6 (109.9) micrograms/l) was normal and did not differ significantly between the iron deficient patients and those with adequate iron.     

Iron status in young Danes. Evaluation by serum ferritin and haemoglobin in a population survey of 634 individuals aged 14–23 yr

Abstract: Iron status was assessed by serum ferritin and haemoglobin in a population survey comprising 634 randomly selected urban Danes (312 males, 322 females) 14–23 yr old. At all ages, males had significantly higher serum ferritin and haemoglobin values than females. Males: median serum ferritin displayed a steady increase with age from 33 to 109 μg/l (r_s=0.53, p<0.0001). The prevalence of absent mobilizable body iron stores (serum ferritin <13 μg/l) was 3.5% at 16–17 yr of age, gradually declining to 0% at 22–23 yr. None of the males had iron deficiency anaemia (serum ferritin <13 μg/l and haemoglobin <129 g/l). Females: median ferritin values displayed a slight increase with age from 28 to 39 μg/l (r_s=0.19, p<0.001). The prevalence of absent iron stores was 12.5% at 16–17 yr of age, declining to 6.6% at 22–23 yr. The prevalence of iron deficiency anaemia (serum ferritin <13 μg/l and haemoglobin <121 g/l) was 4.7% at 16–17 yr of age, declining to 1.3% at 22–23 yr of age. Compared with surveys in other parts of Scandinavia, young Danes had slightly higher serum ferritin levels, and a lower prevalence of iron deficiency.     

Non-invasive liver iron quantification by SQUID-biosusceptometry and serum ferritin iron as new diagnostic parameters in hereditary hemochromatosis

In the HFE-gene era, precise diagnostic parameters remain important to characterize individual iron stores, because the indication for therapy and prognosis are mainly related to the extent of iron loading. The frequently used serum ferritin interferes with non-iron related factors such as inflammation and may produce falsely positive values. We used a SQUID-biosusceptometer in a large series of patients (n = 679) to measure liver iron concentration in the differential diagnosis and therapy control of hereditary hemochromatosis (SQUID = superconducting quantum interference device). This truly non-invasive technique is sensitive, reliable, fast (online results), and also cost-effective when compared to invasive liver biopsy. Recently, ferritin iron content was propagated as a better parameter than ferritin protein. However, we found a poor correlation between ferritin iron and individual liver iron concentrations in patients with iron overload. Ferritin iron saturation varied in a range between 3 and 10%, independent from liver iron concentration. No differences were found between patients with hemochromatosis and secondary iron overload disease. Only patients with liver cell damage had increased ferritin iron saturations. In conclusion the diagnostic values of serum ferritin protein and iron to assess iron overload are limited.