Iron-Deficiency Anemia is Associated With High Concentrations of Transferrin Receptor

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CLIN.CHEM.4 0/5 , 7 74 -7 76 (1 99 4) #{149}e ne ra l C lin ic al Chemistry

77 4 C UN IC AL C HEMIS TR Y, V ol. 4 0, N o.5 , 1994

Iron -Defic iency Anemia Is Associa ted wi th H igh Concen tra tions o f T ransfer rin

Recep to r in Serum

Kari Punnonen ,”3 K erttu Irjala ,1 and A llan Rajam#{228}ki2

We evalu ated the use o f tran sferrin receptor (T fR ) in

serum as an in dex of iron deficiency in 19 pat ients d iag-n os ed a s h av in g iro n-d efic ie nc y a nem ia , in 1 7 p atie nts

with a nem ia o f c hro nic d is ea se , a nd in a c on tro l g ro up o f

19 nonanemic pa ti en ts who underwen t e lec ti ve ocular o r

n asophar yngea l s ur ge ry . The assessmen t o f ir on status

of th e a nem ic patients was based on the presence of

stainable iron on bone marrow e xam in atio n. In th e p a-t ients wi th i ron -de fi ci encyanemia , t he se rum TfR concen -

tra tio n w as 5 .3 ± 1.8 mg/L (mean ± SD), s ign if icant lyhigher than i n the con tro lg roup (1. 7 ± 0 .5 m g/L ) o r i n t he

pa ti en ts w it h anemia o f ch ron ic d isease (1. 6 ± 0.4 m g/L).

This study sugges ts th a t s er um TfR meas uremen t is a

r elia ble index o f ir on dep le tio n and po tentia lly o f impo r-

t ance in the d iagnos is o f i ron -de fi ci encyanemia.

IndexIngTerms: bone marrow staining/ferritin

Iron-deficiency anem ia can be caused by dietary de -

privation of iron or by iron malabsorbtion and may be

th e first clinical sign of increased blood loss. Q uite often ,

iron-deficiency anem ia w arrants extensive inve stig a-

tions of the gastrointestinal tract, given t he r el at iv ely

high probability that u lcers or malignant tumors are

the cause of excessive blood loss. The distinction be -

tween iron-deficiency anem ia and the anem ia that ac-

companies infection, inflammation, or malignancy is not

clear; th e commonly used laboratory tests do not neces-

sarily distinguish these common causes of anemia (1,2).

Conventional laboratory indices of iro n statu s include

serum iron , transferrin/total iron-binding capacity,

transferrin saturation , and ferritin . A lthough each of

these measurements has m erit, no single determination

gives a reliable index of iron status (2-4). H i g h sensi-

tiv ity as well as specificity are of s pe ci al im p or ta nc e fo r

a test of iron status, because further identification of the

cause of depletion of iron stores requires tedious clin ical

a nd la boratory inve stig ations. The absence of stainable

iron on bone marrow exam ination is generally regarded

as the only reliab le i n d e x of iron d e f i c i e n c y .

Iron delivery to erythroblasts is m ediated by the in-

teraction of plasma transferrin with cell surface trans-ferrin receptors (T ifis) (5, 6). The T ifi protein ha s tw o

identical polypeptide chains, 95 kDa each, and is pre-

sent on the surfaces of virtually all cells. In norma l

a du lt s, h ow ev er , -80% of th e receptors are in the eryth-

roid marrow (5). The number of TfRa on the c el l s ur fa ce

Departments of ’ C li ni ca l C h em i st ry and2 Hematology, Univer-sity C en tral H ospital o f T urk u, Kiinamyllynkatu 4 -8 , 2 05 20T urk u, F in la nd .

3Address correspondence to this author. Fa x 358-21-613920.Received October 4, 1 99 3; accep ted Jan uary 8, 19 94 .

reflects th e iro n req uire me nt (7). Deprivation of iron

resu lts in prompt induction of TIR synthesis (7). SolubleTfR ha s been i d e n t i f i e dn human serum and pla sm a; it

is a truncated form of tissue receptor, w ith th e trunca-

tion occurring at a site just beyond the cell m em brane

(8). R ecently, serum concentrations of T have been

suggested as a reliab le index of iron depletion (2, 6,

9-13). In earlier studies of iron depletion , the iron sta-

tus was not confirmed by bone m arrow exam ination.

Therefore, w e analyzed serum TfR in a g r o u p o f a nemic

p atien ts, an d correlated the T concentrations w ith the

type of anemia an d presence of s t a i n a b l e iron in bone

marrow.

Subjects and Me thods

Patients. A total of 36 anem ic patients participated in

th is study. Bone marrow exam inations w ere performed

on all patients to identi1y the type of anem ia an d to

study the iron stores. A ll procedures were in accordance

with the H elsinki D eclaration of 1975 , as revised in

1983 . On the basis of bone m arr ow e xamin atio ns , 19

patients (13 women and 6 men) who fu lfilled the mor-

phological cr iteria of iron defic iency and who ha d no

sta inable iron on bone marrow exam ination were de -

fined as having iron-defic iency anem ia. For a contro l

group , we used 19 age- an d sex-m atched patients (13

women and 6 men) who underwent elective ocu lar or

nasopharyngeal surgery. N o bone m arrow exam inations

were perform ed on these patients but, to exclude pa-

tients w ith anem ia or acute inflammation , w e checked

t he ir h emo gl ob in , erythrocyte indices, erythrocyte sod-

iinentation rate, and serum C-reactive protein concen-

trations and found them to be within the reference in-

tervals. Another 17 anem ic patients (10 wom en and 7

m en) were selected on the basis of bone marrow exam -

inations to form the group defined as having anem ia of

chronic disease. These patients had sta inable iron on

bone marrow exam ination (m edian storage iron 2+,

range 1+ to 4+ on a scale from 0 to 4+), and their

sideroblast count ranged from 5% to 15% . O f the 17

patients w ith chronic d isease , 8 ha d recu rre nt o r ch ron ic

infections, and the remaining 9 patients had other con-ditions related to m iscellaneous chronic d iseases.

Methods. Bone marrow was asp irated from the ster-

num , and sm ears w ere stained by the M ay-G rilnwald-

G iem sa m ethod (sta in provided by Orion D iagnostica ,

H elsink i, F in land); the iron stores were stained by the

Prussian blue m ethod . B lood counts were measured

w ith an automated analyzer (Technicon H*2; M iles,

Tarrytown, NY). Serum Tifi wa s assayed w ith a com -

m er cia lly a va ila ble kit based on a polyclonal antibody

in a sandw ich enzym e im munoassay form at (C lin igenT11;

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iron-deficiencyControls anem ia

19 19

Anemia ofc hr on ic d is ea se

17

zmol (Fe)/g (transferlin).

CL IN ICALCHEM ISTRY , Vo l. 4 0 , No . 5 , 1994 775

R& D Systems, M inneapolis, M N). T he r ef er en ce range

provided by the k it m an ufa ctu re r for T analysis is

1.54 ± 0.43 mg/L (n = 1 00 0) . F er ritin w as m easured

(reference range 15-306 igfL for m en, 5-103 /LgIL for

women, according to the manufacturer) w ith an IRMA

(Spectria; Or io n D ia gn os ti ca ). Transferrin w as mea-

sured [reference range 2.1-3.4 g /L for m en, 2 .0-3.1 g/L

for w om en (14)] with a Behring Nephelom eter (Beh-

ringw erke, M arburg, G erm any) and antibodies provided

by D akopatts (G lostrup, D enm ark). Serum ir on ( re fe r-ence range 10-40 moIIL) w as m easured w ith an Iron

FZ assay (H offm ann-LaR oche, B asel, Sw itzerland),

based on a guanidine h yd ro ch lo rid e/fe rr oz in e r ea ct io n.

The transferrin index (TI) was calculated as iron (tm o1/

L)/transferrin (g/L ), as recently suggested by Beilby et

al . (15).

Resul ts and D iscuss ion

We analyzed serum T if i c on ce nt ra tio ns an d per-

formed convent ional laboratory tests in anem ic patients

an d correlated th e results w ith the type of anem ia and

presence of iron in bone marrow . A tota l of 36 anem ic

patients participated in this study, and the resu lts forb lood counts and iron status markers ar e presented in

Table 1 . Common practice in F in land includes m easur-

ing the complete blood count, serum iron , transferrin,

and ferritin when exam ining anem ic patients. In pa-

tients w ith no chronic disease these values have been

helpfu l in clinical d ecision -m ak in g. H ow ever, acute-

phase responses make the interpretation of the labora-

tory d ata difficult, given that both serum ferritin and

serum transferrin are acute-phase reactan ts, th e form er

increasing and the latter decreasing in acute illness (3 ,

1 4, 16 -1 8). Serum iron concentration is lower in pa-

tients w ith iron-defic iency anem ia than in healthy sub-

jects, but it cannot be used t o d is tin gu is h ir on -d ef ic ie nc y

anem ia from anem ia of chronic disease. In the present

study the mean seru m transferrin con cen tration was

slightly h igher in the patients w ith iron-deficiency ane-

m ia than in the controls (Table 1), but the iron satura-

tion of tra nsferrin calculated as the T I is m ore useful

th an either serum iron or serum tran sferrin alon e (15)

(F ig . 1 , top). T he mean serum ferritin concentration w as

low er in patients w ith iron-deficiency anem ia (9 ± 6

mean ± SD ) than in the controls (72 ± 89 1 zg/L ,

Table 1. Ma rk er s o f ir on status in anem i c patients andcon tro ls (mean ± SD).

Hemoglobin,g/L 138 ± 13 89 ± 19 10 3 ± 13

Meanceltvolume,fL 91±4 73±9 90±7

iron, moI/L 17.3 ± 6.3 4.3 ± 2. 5 7. 1 ± 4.0

Transferrin, g/ L 2.5 ± 0.4 3.3 ± 0.5 1.9 ± 0.5

TI 7. 1 ± 2.7 1.3 ± 1.0 3.7± 1. 5

Ferritin, Lg/L 72 ± 89 9 ± 6 28 8 ± 274

TfR, mg/L 1.7 ± 0.5 5.3 ± 1.8 1.6 ± 0.4

a

A

aA

A A

Vv; kA

X fv

ABC ABC ABC

Transferrin T I Ferritin

Transferr inReceptor (mgIL)

F ig . 1 . Serum concentrat ions of t ransfemn, TI , and fer ri tin (top), an d

of TfR (bottom) i n t h e thr ee g roups : A, c on tr ols ( n 19): 8, patients

with iron-deficiency a nemia ( n = 19): an d C, patientsw i th anem i a ofc hr on ic d is ea se ( n = 17).

mean ± SD), but was sign ifican tly inc rease d in the

patients w ith anem ia of chronic disease (288 ± 27 4

pgIL) (Table 1). Thus, the us e of ferritin as a marker of

iron defic iency is complicated by the acute-phase re -

sponses associated w ith chronic d isease.

W e evaluated the use of serum TfR as an index of body

iron status in anem ic patients and correlated the T

concentration w ith the presence of iron stores in bonemarrow . The individual values of transferrin, TI, fer-

ritin, and T are shown in Fig . 1. In the patients who

h ad an em ia fulfilling the m orphological criter ia of iron-

defic iency anem ia and no stainable iron on bone m a r r o w

exam ination, the serum TfR concentration w as 5 .3 ± 1. 8

m gfL , sign ifican tly high er than that in the control group

(1.7 ± 0.5 mgfL). In 18 of the 19 patients w ith iron-

defic iency anem ia, the serum TfR concentration was

higher than in an y of the control subjects. In the pa-

tients w ith anem ia of chronic d isease (and readily stain-

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77 6 CUN ICAL CHEMISTRY , V ol. 4 0, N o. 5, 1994

a b l e i ron in bon e marrow), th e serum T ifi con cen tration

was 1. 6 ± 0. 4 mg/L, essential ly equal to that in the

co ntro l g ro up . The values in the control group w ere w ell

within the reference range provided by the kit m anu-

facturer. Earlier studies have varied considerably in the

concentrations reported for serum and plasma T, ap-

parently because of the d ifferent specificities of the an-

tib od ies th ey used (6).

Clearly, a m ore specific index of iron-deficient eryth-

ropoiesis is needed . Serum concentrations of T haveb een sug gested to reflect the availability of iron for

erythropoiesis (1 , 10, 11). So fa r no published studies

have correlated the serum TIE concentrations w ith the

true iron status (based on bone marrow exam ination). In

the present study, we found that h igh serum TIE con-

centrations could effectively identify the patients w ith

true iron defic iency (confirm ed on the basis of absence of

stainable iron in bone marrow ) and that serum TIE

m easurem ents could also distinguish patients w ith iron-

d eficien cy a ne mia from those w ith anem ia of chronic

d isease. TIE measurem ent seem s to provide a means of

identifying iron depletion even in patients w ith acute-

phase reactions associated w ith inflam matory condi-tions (1,2); however, the effectiveness of TI E measure-

m ents in identifying latent iron deficiency remains to be

evaluated. E arlier studies reported increased TIE con-

centrations in association w ith , e.g., increased erythro-

poiesis, hem olytic anem ias, and acute leukem ias (2, 13,

19 , 20). However, none of these conditions generally

constitutes a clinical problem in the identification of

iron-deficiency anemia. On the basis of the present

study, consistent w ith other previous reports (1,2, 10),

w e c on clu de that the serum TIE concentration is a use-

ful serum marker of iron depletion.

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16 . Leggett BA , Brown NN , Bryant S J, D uplock L, P ow ell LW ,H allid ay ,JW. F ac to rs a ff ec ti ng th e concentrations of ferritin inserum in a healthy Australian population . C lin Chem 1990;36:1350-5.17 . Witte DL. Can serum ferritin be effectively interpreted in th epresence of the acute-phase re sp on se ? [ Ed it or ia l] . Clin Chem1991;37:484-5.

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