Serum Transferrin Receptor

8/13/2019 Serum Transferrin Receptor

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1997 89: 1052-1057

Kari Punnonen, Kerttu Irjala and Allan Rajamki

of Iron DeficiencySerum Transferrin Receptor and Its Ratio to Serum Ferritin in the Diagnosis

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Serum Transferrin Receptor and Its Ratio to Serum Ferritin in theDiagnosis of Iron Deficiency

By Kari Punnonen, Kerttu Irjala, and Allan Rajama ki

The objective of the study was to evaluate the diagnostic sis of iron deficiency anemia (AUCROC 0.98). Serum ferritin

efficiency of laboratory tests, including serum transferrin re- measurement also distinguished between IDA patients and

ceptor (TfR) measurements, in the diagnosis of iron deple- ACD patients. However, the optimal decision limit for evalu-tion. The patient population consisted of 129 consecutive ation of ferritin measurements was considerably above theanemic patients at the University Hospital of Turku who conventional lower reference limits, complicating the inter-

were given a bone marrow examination. Of these patients, pretation of this parameter. Calculation of the ratio TfR/log48 had iron deficiency anemia (IDA), 64 anemia of chronic ferritin (TfR-F Index) is a way of combining TfR and ferritindisease (ACD), and 17 patients had depleted iron stores and results. This ratio provided an outstanding parameter for thean infectious or an inflammatory condition (COMBI). Deple- identification of patients with depleted iron stores (AUCROC

tion of iron stores was defined as a complete absence of 1.00). In anemic patients, TfR measurement is a valuablestainable iron in the bone marrow examination. Serum TfR noninvasive tool for the diagnosis of iron depletion, and of-concentrations were elevated in the vast majority of the IDA

fers an attractive alternative to more conventional labora-and COMBI patients, while in the ACD patients, the levels

tory tests in the detection of depleted iron stores.were within the reference limits reported earlier for healthy

1997 by The American Society of Hematology.subjects. TfR measurement thus provided a reliable diagno-

T been introduced as a promising new tool for the diagnosisof iron depletion.3,6-11HE LEVEL of body iron stores is affected both bydietary intake and by the physiological need of ironfor erythropoiesis. Consequently, iron deficiency anemia The TfR receptor is a transmembrane protein with two

identical polypeptide chains, each weighing 95 kD; iron de-(IDA) can be caused by dietary deprivation of iron or by

iron malabsorbtion; importantly, it may be the first clinical livery to erythroblasts is mediated by the interaction ofplasma transferrin with cell surface transferrin receptors.11,12sign of increased blood loss. Unexplained iron deficiency

anemia warrants extensive investigations of the gastrointesti- From the cell membrane the TfR-transferrin-iron complex is

internalized via an endocytic vesicle, and in the intracellularnal tract, since the probability of ulcers or malignant tumors

as the cause of excessive blood loss is relatively high.1 Using compartment iron dissociates from TfR-transferrin com-

plex.3,11,13 The iron remains in the cytosol, while the TfR-laboratory tests, distinguishing between iron deficiency ane-

mia and the anemia that accompanies infection, inflamma- transferrin complex is recycled back to the cell surface. Vir-

tually all cells have transferrin receptors on their surface, buttion, or malignancy is difficult, as the commonly used labora-

tory parameters do not necessarily distinguish between these in the normal adult, about 80% of them are in the erythroid

marrow.12 Soluble TfR present in human plasma is a trun-common causes of anemia.2-5 The conventional laboratory

tests of iron status, serum iron, transferrin/total iron-binding cated form of the tissue receptor and exists as a transferrin-

receptor complex.13-15 The TfR number on the cell surfacecapacity (TIBC), transferrin saturation, and ferritin are

widely used in clinical practice, although they are consider- reflects the iron requirement, and iron deprivation has been

shown to result in the prompt induction of transferrin recep-ably influenced by acute phase responses, which complicates

the clinical interpretation of the test results.3-5 High sensitiv- tor synthesis.16

We have evaluated the clinical efficiency of TfR measure-ity, as well as specificity, is of special importance for a test

of iron status, as the further identification of the cause of ments in the identification of iron deficiency in an extensive,

consecutive patient population. The diagnostic classificationthe depletion of iron stores is bound to result in tedious

clinical and laboratory investigations. Because the absence of all patients was based on an examination of bone marrow

using iron staining as the gold standard for iron depletion.of stainable iron in bone marrow examination is generally

regarded as the definitive marker of iron deficiency, marrow

examinations are generally requested to confirm iron defi- MATERIALS AND METHODSciency. There is an evident clinical need for noninvasive and Patients. The patient population consisted of 129 consecutivesensitive means for the detection of iron deficiency, and in anemic adult patients at the University Hospital of Turku who under-recent years, the serum transferrin receptor (TfR) level has went a bone marrow examination because of anemia. The purpose

of the examinations was to define the type of anemia and to deter-

mine iron stores. Anemia was defined as a hemoglobin concentration

of less than 128 g/L in men and 117 g/L in women, which constitutesFrom the Central Laboratory, Departments of Clinical Chemistry

and Hematology, University Hospital of Turku, Turku, Finland. the lower 2.5% reference limits in our hospital. All blood sampleswere obtained before any blood transfusions, and patients on oralSubmitted March 14, 1996; accepted September 16, 1996.

Address reprint requests to Kari Punnonen, MD, PhD, Depart- iron therapy were excluded from the study population. Patients with

hematological malignancies were also excluded from this study, asment of Clinical Chemistry, University Hospital of Turku, Kiinamyl-

lynkatu 4-8, 20520 Turku, Finland. certain hematological malignancies have been reported to be associ-

ated with an elevated serum TfR regardless of the iron status of theThe publication costs of this article were defrayed in part by page

charge payment. This article must therefore be hereby marked patients.14,17 Additionally, patients who had hemolytic anemia or

defined deficiency of vitamin B12 or folic acid were excluded fromadvertisement in accordance with 18 U.S.C. section 1734 solely to

indicate this fact. the study population, as these conditions may be associated with

elevated TfR levels irrespective of iron status.18 The patients were 1997 by The American Society of Hematology.

0006-4971/97/8903-0013$3.00/0 assigned to one of three groups on the basis of the bone marrow

1052 Blood, Vol 89, No 3 (February 1), 1997: pp 1052-1057

AID Blood 0026 / 5h2c$$$501 12-30-96 14:23:43 blda WBS: Blood

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TRANSFERRIN RECEPTOR AND IRON DEFICIENCY 1053

Table 1. Laboratory Tests of Iron Status RESULTSin the Three Anemic Patient Groups

The results for blood counts and iron status markers forIDA (n 48) ACD (n 64) COMBI (n 17) the 129 anemic patients are summarized in Table 1. Serum

Hemoglobin, g/L 93 { 16 (96) 102 { 12 (103) 88 { 20 (90) iron was not a reliable indicator of iron depletion (Table 2).MCV, fl 75 { 9 (75) 90 { 7 (91) 78 { 9 (79) When the study population was analyzed as a whole (n Iron, mmol/L 8 { 11 (4) 10 { 6 (9) 6 { 3 (6)

129), serum transferrin distinguished fairly well betweenTransferrin, g/L 3.3 { 0. 4 ( 3. 3) 1 .9 { 0. 5 (1 .8) 2. 6{ 0.6 (2.4)

iron-deficient and ACD patients (Table 2). However, in aFerritin, mg/L 21 { 55 (11) 342 { 3 85 ( 19 5) 8 7{ 167 (23)TfR, mg/L 6.2 { 3. 5 ( 5. 0) 1 .8 { 0. 6 (1 .8) 5. 1{ 2.0 (4.7) considerable proportion of the iron-deficient patients, theTI 2.7 { 3. 9 ( 1. 3) 5 .2 { 2. 9 (4 .9) 2. 7{ 1.6 (1.8) transferrin concentration was within the reference limits ofTransferrin saturation, % 12 { 17 (5.7) 23 { 13 (21) 12 { 7 (8)

a healthy population (see Materials and Methods), makingTfR/log ferritin 6.8 { 6. 5 ( 5. 4) 0 .8 { 0. 3 (0 .8) 3. 8{ 1.9 (3.2)

the clinical interpretation of the transferrin concentrationsResults are mean { SD (median).

difficult. The area under the ROC curve (AUCROC) provided

by Transferrin-Index (TI, iron/transferrin),21 or the percent-

age transferrin saturation [iron/(transferrin 1 23) 1 100] inexamination and clinical data. Forty-eight patients (32 women andthe identification of iron-deficient patients was 0.82. For16 men) who fulfilled the morphologic criteria of iron deficiencycomparison, the corresponding AUCROC for red cell meanand who had no stainable iron in the bone marrow were classified

as having IDA. Sixty-four anemic patients (37 women and 27 men) corpuscular volume (MCV) was 0.88.were classified as having anemia of chronic disease (ACD), and In male and female IDA patients, the median serum ferri-these patients all had stainable iron in the bone marrow. Of these tin concentrations were 13 mg/L (mean { standard deviation64 patients, 34 had recurrent or chronic infections, while the re- [SD], 37 { 94) and 9 mg/L (mean { SD, 12 { 9), respec-maining 30 had other chronic diseases (ie, nonhematological malig- tively. In male and female ACD patients, the median ferritin

nancies and inflammatory diseases such as rheumatoid arthritis). concentrations were 195 mg/L (mean { SD, 364 { 310)Those patients who had no iron in the bone marrow together withand 169 mg/L (mean { SD, 326 { 440), respectively. There

an infectious disease, a chronic inflammatory disease (eg, rheumatoidhave been no previous reports of any significant differencesarthritis or colitis ulcerosa) or a nonhematological malignancy werein TfR concentrations between male and female patients; theplaced in a COMBI group (n 17). In addition, two iron-deficientpresent findings are consistent with this, as for instance, inpatients who had a C-reactive protein (CRP) value above 20 mg/L

were regarded as having an accompanying inflammatory or infec- male and female ACD patients, the median TfR concentra-tious condition and were included in the COMBI group. Preliminary tions were 1.9 g/L (mean { SD, 1.9 { 0.7) and 1.7 g/Lresults concerning a small subgroup of the patients (n 36) have (mean { SD, 1.8 { 0.5), respectively. As neither ferritinbeen reported earlier.19 nor TfR concentrations differed significantly between male

Samples and analytical methods. Bone marrow was aspirated and female patients, the results have been analyzed and pre-from the sternal bone or iliac crest. The smears were stained using

sented without distinction between male and female patients.the May-Grunwald-Giemsa method (Orion Diagnostica, Helsinki,

Serum ferritin measurements distinguished between IDA andFinland), and the iron stores were stained by the Prussian blue

ACD patients (AUCROC 0.98); however, the optimal decisionmethod. Blood counts were measured with an automated analyzerlimit for the interpretation of ferritin measurements was con-(Technicon H*2, Technicon Instruments Corp, Tarrytown, NY). Se-siderably above the conventional lower reference limit,rum transferrin receptor assays were performed using a commercially

available kit based on a polyclonal antibody in a sandwich enzyme which is based on evaluations of apparently healthy popula-immunoassay (EIA) format (Clinigen; R&D Systems, Minneapolis, tions (Tables 1 through 3 and Fig 1). TfR concentrationsMN). According to the assay kit from the manufacturer, the central were elevated in the vast majority of IDA and COMBI pa-95th percentile of the reference distribution of TfR concentration is tients, and the serum TfR concentration was found to be a0.85 to 3.05 mg/L (n 1,000). Ferritin (reference range, 15 to good indicator of iron deficiency, as demonstrated by the306 mg/L for men, 5 to 103 mg/L for women, according to the

manufacturer) was measured using a radioimmunoassay (Spectria,

Orion Diagnostics). Transferrin (reference range, 2.1 to 3.4 g/L forTable 2. AUCROC Values (SE) for Parameters of Iron Statusmen, 2.0 to 3.1 g/L for women20) was measured with a Behring

Nephelometer (Behringwerke AG, Marburg, Germany) together with IDA / COMBI vACD IDA vAC D COM BI vACDantibodies provided by Dakopatts (Dakopatts, Glostrup, Denmark).

MCV 0.89 (0.03) 0.90 (0.03) 0.86 (0.05)Serum iron (reference range, 10 to 40 mmol/L) was measured using

Iron 0.71 (0.05) 0.71 (0.05) 0.68 (0.07)an Iron FZ assay (Hoffmann-LaRoche, Basel, Switzerland) based

Transferrin 0.94 (0.02) 0.98 (0.01) 0.84 (0.05)on a guanidine hydrochloride/Ferrozine reaction. The transferrin in-

TI (iron/transferrin) 0.82 (0.04) 0.84 (0.04) 0.79 (0.06)dex (TI) was calculated as iron (mmol/L)/transferrin (g/L), as re-Ferritin 0.96 (0.02) 0.98 (0.01) 0.89 (0.07)

cently suggested by Beilby et al.21 Percent transferrin saturation wasTfR 0.98 (0.01) 0.98 (0.01) 0.98 (0.01)

calculated as [iron/(transferrin 1 23)] 1 100.TfR/ferritin 0.98 (0.01) 1.00 (0.00) 0.94 (0.04)Statistical analysis. Receiver operating characteristics (ROC)TfR/lo g ferritin 1.00 (0.001 ) 1 .0 0 (0.00 ) 1.00 (0.01)

curves were visualized and the corresponding areas under the curves

were calculated using the GraphROC for Windows software pack- Separate values concerning the identification of patients with de-

pleted iron stores have been calculated for the whole patient popula-age.22 The areas under the ROC curves (AUCROC) were compared

with each other using a software mathematically based on a method tion (IDA / COMBI vACD), for the population containing patients

with uncomplicated IDA patients and ACD patients (IDA vACD), anddescribed earlier.23-25 The P values (one-tailed test) corresponding

to the calculated z scores were drawn from a table of normal distribu- for the patient population in which all had an infectious or inflamma-

tory disease (COMBI vACD).tions.




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PUNNONEN, IRJALA, AND RAJAMA KI1054

Table 3. Ability of Ferritin, TfR, TfR/Ferritin Ratio and TfR-F Index to Identify Patients With Iron Deficiency

IDA vACD IDA / COMBI vACD COMBI vACD

TfR 1 100/ TfR 1 100/ TfR 1 100/

Ferritin TfR Ferritin TfR-F Index Ferri tin TfR Ferri ti n TfR-F Index Ferritin TfR Ferritin TfR-F Index

False negative 1 3 1 0 6 4 3 1 5 1 2 1

False positive 1 4 1 0 1 4 1 0 1 4 1 0

True negative 63 60 63 64 63 60 63 64 63 60 63 64

True positive 47 45 47 48 59 61 62 64 12 16 15 16

Sensitivity 0.98 0.94 0.98 1.00 0.91 0.94 0.95 0.98 0.71 0.94 0.88 0.94

Specificity 0.98 0.94 0.98 1.00 0.98 0.94 0.98 1.00 0.98 0.94 0.98 1.00

Positive PV 0.98 0.92 0.98 1.00 0.98 0.94 0.98 1.00 0.92 0.80 0.94 1.00

Negative PV 0.98 0.95 0.98 1.00 0.91 0.94 0.95 0.98 0.93 0.98 0.97 0.98

Efficiency 0.98 0.94 0.98 1.00 0.95 0.94 0.97 0.99 0.93 0.94 0.96 0.99

An efficiency curve for the distinction between ACD and IDA patients was generated for each parameter, and the maximum point of the curve

was used as a cutoff limit in all patient populations. The cutoff limits based on the efficiency curves were 41 mg/L for ferritin, 2.7 mg/L for TfR,

4.5 for TfR 1 100/ferritin, and 1.5 for the TfR-F Index. PV predictive value.

scattergram in Fig 2 and by the ROC curve in Fig 3 (AUC ROC tients more effectively than ferritin measurements (P

.033).0.98). In the ACD patients, the levels were within the refer-

ence limits reported earlier for healthy subjects.19 TfR mea- Earlier, the calculation of the TfR/ferritin ratio was re-

ported to reflect the depletion of iron stores in response tosurements effectively identified iron deficiency, even in thepresence of an accompanying inflammatory or infectious phlebotomies.7 In the present patient material, the calculation

of the TfR/ferritin ratio as such only slightly improved diag-condition (Tables 2 and 3, Fig 2); furthermore, the statistical

comparison of the ROC curves indicates that TfR measure- nostic sensitivity and specificity compared with the use of

TfR or ferritin alone (Tables 2 and 3). However, both sensi-ments distinguished between the COMBI and the ACD pa-

tivity and specificity were improved by logarithmic transfor-

Fig 1. Serum ferritin concentrations in anemic patients. IDA (iron-

deficiency anemia) (n ! 48) and ACD (anemia of chronic disease) (n

! 64). Those patients who had depleted iron stores together with an

infectious disease, a chronic inflammatory disease, or a nonhemato-

logical malignancy were assigned to the COMBI group (n ! 17). The Fig 2. Serum TfR concentrations in anemic patients. For abbrevia-

tions, see text to Fig 1. The central 95th percentile of the referencelower reference limits of the serum ferritin assay are indicated sepa-

rately for male () and female () subjects by horizontal bars. distribution for the TfR assay is shown with horizontal bars.




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consisting of consecutive anemia patients subjected to a bone

marrow examination. Iron deficiency was defined as a com-

plete absence of stainable iron in bone marrow.

Serum iron and iron saturation of transferrin are of limited

value in the diagnosis of IDA, as the corresponding AUCROC

values, consistent with earlier studies,26 do not reflect proper

diagnostic sensitivity and specificity. This is apparently due

to the interference of the acute-phase response in serumiron and transferrin concentrations. Serum ferritin has been

widely used to define iron depletion. In this study population,

ferritin measurements (AUCROC 0.98) and even serum trans-

ferrin (AUCROC 0.98) distinguished effectively between pa-

tients with uncomplicated IDA and those with ACD, but the

optimal decision limit for the interpretation of both ferritin

and transferrin measurements was found to be considerably

above the conventional reference limits, which are based on

the evaluation of apparently healthy populations. It is evident

that the ability of ferritin to distinguish between IDA and

ACD is due not only to the decrease in serum ferritin level

in IDA patients but, to a considerable extent, to the increase

in serum ferritin caused by the acute phase responses associ-

ated with chronic inflammatory disease. The ROC curvesproduced on the basis of the present patient material (Table

2) are in good agreement with those generated earlier on

the basis of meta-analysis for ferritin and iron saturation of

transferrin.26 Based on the present data, it can be statistically

Fig 3. ROC curves for TfR, ferritin, and TfR-F Index (TfR/log ferritin

ratio) in the identification of iron-deficient patients. The ROC curves

are shown separately for the whole patient population (n ! 129) (A)

and for the distinction between the ACD (n ! 64) and COMBI (n !

17) patients (B). TfR-F Index -, TfR

, ferritin .

mation of the ferritin value, and we suggest that this parame-

ter be referred to the TfR-Ferritin Index (TfR-F Index). The

calculation of the TfR/log ferritin ratio (TfR-F Index) pro-vided an outstanding parameter for the identification of iron-

deficient patients (Table 3, Figs 3 and 4). When the whole

study population (n 129) was analyzed, the TfR-F Index

provided an AUCROC value of 1.00. Consequently, when

subgroups were analyzed, the AUCROC values were 1.00 for

the distinction between the ACD (n 64) and IDA groups

(n 48), and 1.00 for the distinction between the ACD and

COMBI groups (n 17) (Tables 2 and 3, and Figs 3 and

4).

DISCUSSION

The clinical situation in which serum transferrin receptor

(TfR) measurements have been suggested to be especially

useful is the differentiation between IDA and ACD.2,11 Thedistinction between IDA and the anemia that accompanies

infection, inflammation, or malignancy is difficult, as the

laboratory parameters commonly used do not necessarily

distinguish these common causes of anemia. In the present

study, we have evaluated the clinical efficiency of both TfR

measurements and a variety of more conventional laboratoryFig 4. The TfR-F Index (TfR/log ferritin ratio) in anemic patients.

tests in the identification of patients with iron deficiency.For explanation of the abbreviations, see text in Fig 1. The median

Every attempt was made to avoid any bias due to preselection values for each patient group (IDA, 5.4; COMBI, 3.2; ACD, 0.8) areindicated by horizontal bars.of patients by using a clinically relevant study population




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PUNNONEN, IRJALA, AND RAJAMA KI1056

estimated22 that in anemic patients who do not have an ac- nation of TfR and ferritin measurements provides the highest

sensitivity and specificity. It may be predicted that thesecompanying infection or inflammatory disease, a cut-off

limit of 41 mg/L for serum ferritin provides optimal diagnos- measurements are likely to replace the conventional parame-

ters of iron status, ie, serum iron, transferrin, and ferritintic efficiency. However, this estimation is apparently no

longer valid if we assume that the iron-deficient patient has alone, in clinical laboratories. They would be especially use-

ful at outpatient clinics, where bone marrow examinationsanother disease accompanied by an acute phase reaction (ie,

the COMBI group), so that the diagnostic usefulness of ferri- are often either not available or are regarded as an invasive

means of identifying patients with depleted iron stores.tin measurements is reduced (Tables 2 and 3). In the interpre-tation of ferritin results, the conventional population-based

reference limits are not very useful, as for instance in femaleREFERENCES

IDA patients (n 32), the lower reference limit of ferritin1. Rockey DC, Cello JP: Evaluation of the gastrointestinal tractconcentrations provided only 22% sensitivity in the identifi-

in patients with iron-deficiency anemia. N Engl J Med 329:1691,cation of iron deficiency. On the other hand, it is obvious

1993that the need for disease-specific decision limits is difficult

2. Ferguson BJ, Skikne BS, Simpson KM, Baynes RD, Cookto meet. In conclusion, the measurement of serum ferritin JD: Serum transferrin receptor distinguishes the anemia of chronicmay provide a rational basis for the identification of iron disease from iron deficiency anemia. J Lab Clin Med 119:385, 1992deficiency; the interpretation of the ferritin levels, however, 3. Cazzola M, Beguin Y: New tools for clinical evaluation ofrequires careful diagnostic classification of the patients and erythron function in man. Br J Haematol 80:278, 1992

4. Harju E, Pakarinen A, Larmi T: A comparison between serumknowledge of all the factors that may cause changes in serumferritin concentration and the amount of bone marrow stainable iron.ferritin levels.Scand J Clin Lab Invest 44:555, 1984The proinflammatory cytokines tumor necrosis factor-a

5. Burns ER, Goldberg SN, Lawrence C, Wenz B: Clinical utilityand interleukin-6 have been suggested to reduce TfR expres- of serum tests for iron deficiency in hospitalized patients. Am J Clinsion under in vitro experimental conditions.27 On the basis of

Pathol 93:240, 1990the present study, TfR measurements are able to distinguish

6. Kohgo Y, Niitsu Y, Kondo H, Kato I, Tsushima N, Sasaki K,between patients with IDA and those with ACD. The finding Hirayama M, Numata T, Nishisato T, Urushizaki I: Serum transferrinsuggests that in ACD patients the potentially increased cyto- receptor as a new index of erythropoiesis. Blood 70:1955, 1987kine production does not greatly affect the TfR response 7. Skikne BS, Flowers CH, Cook JD: Serum transferrin receptor:caused by iron depletion; this is consistent with earlier re- A quantitative measure of tissue iron deficiency. Blood 75:1870,

1990ports.2 A major advantage of TfR measurements over serum8. Flowers CH, Skikne BS, Covell AM, Cook JD: The clinicalferritin is the apparent specificity of the biological response

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Variations in serum erythropoietin and transferrin receptor duringlysis or megaloblastosis can be excluded, the TfR measure-

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Annu Rev Med 44:63, 1993good estimate of body iron in individual subjects, 7 but no12. Huebers HA, Finch CA: The physiology of transferrin andstudies of a representative patient population have so far

transferrin receptors. Physiol Rev 67:520, 1987been published. In the present study, we evaluated a variety13. Ahn J, Johnstone RM: Origin of a soluble truncated transferrinof possibilities of combining the TfR and ferritin parameters;

receptor. Blood 81:2442, 1993the results suggest that calculation of the TfR/ferritin ratio

14. Huebers HA, Beguin Y, Pootrakul P, Einspahr D, Finch CA:does not considerably improve diagnostic efficiency com-

Intact transferrin receptors in human plasma and their relation topared with TfR alone (Tables 2 and 3). However, logarithmic erythropoiesis. Blood 75:102, 1990transformation of the ferritin values and calculation of the 15. Shih YJ, Baynes RD, Hudson BG, Flowers CH, Skikne BS,TfR/log ferritin ratio (the TfR-F Index) provided an out- Cook JD: Serum transferrin receptor is a truncated form of tissue

receptor. J Biol Chem 265:19077, 1990standing indicator of iron depletion, as demonstrated by the

16. Rao KK, Shapiro D, Mattia E, Bridges K, Klausner RD:scattergram and the corresponding ROC curves (Figs 3 andEffects of alterations in cellular iron on biosynthesis of the transferrin4). This TfR-F Index takes advantage of the relationshipreceptor in K562 cells. Mol Cell Biol 5:595, 1985between two phenomena, ie, an increase in TfR and a de-

17. Beguin Y, Lampertz S, De Groote D, Igot D, Malaise M,crease in the ferritin concentration. This parameter consistsFillet G: Soluble CD23 and other receptors (CD4, CD8, CD25,

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Serum Transferrin Receptor

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