LETTER TO THE EDITOR
Characteristics of non-anemic healthy adolescents
with serum-soluble transferrin receptor concentrations
outside the reference interval
Yong Hoon Jun
&
Chung Hyun Nahm
&
Jong Weon Choi
Received: 2 April 2007 / Accepted: 1 February 2008 / Published online: 27 February 2008
#
Springer-Verlag 2008
Dear Editor,
Iron transport in the body is carried out by the binding of
iron to a specific carrier protein, transferrin. The transferrin
receptor (TfR) mediates the flow of serum iron from the
extracellular pool into the cytoplasm by receptor-mediated
endocytosis [1]. Virtually, all cells have TfR on their
surface, but most of TfR are located in the erythroid
precursors of the bone marrow and the peripheral immature
reticulocytes. Serum-soluble transferrin receptor (sTfR) is a
truncated monomer of tissue receptor, which circulates in
the form of a complex of transferrin and its receptor [2].
The sTfR has been suggested as a good estimate of body
iron status and a biochemical maker of iron-deficient
erythropoiesis [3, 4]. Increased sTfR concentrations are
usually observed in iron deficiency anemia (IDA), or in
cases of iron depletion in tissues, because iron deprivation
induces a synthesis of TfR. Conditions associated with
erythroid hyperplasia, such as immune hemolytic anemia
and thalassemia, can also increase the value of sTfR,
irrespective of body iron status [5].
Healthy subjects, who had no evidence of iron depletion
and hemolytic anemia, sometimes exhibit a higher sTfR
concentration than the patients with iron deficiency.
Similarly, some IDA patients show much more diminished
sTfR concentrations than non-anemic individuals. In the
previous study, we reported that IDA patients who were not
accompanied by an increase in sTfR levels are linked to the
diminution of immature reticulocyte production [6]. There
have been few studies that have closely examined the
healthy subjects with serum sTfR concentrations outside
the reference interval. In the current study, we investigated
the features of the non-anemic healthy individuals, who
did not reach the lower limit or exceeded the upper limit
of the reference range in serum sTfR levels.
A total of 92 healthy adolescents (49 males and 43
females) with a median age of 18 years (range 17–19 years),
who displayed the abnormal results in serum sTfR concen-
trations but showed no evidence of anemia, iron depletion,
or hemolytic diseases, were enrolled. Adolescents showing
normal values in serum iron parameters (serum ferritin
>12 μg/l; serum iron >50 μg/dl) and normal hemoglobin
levels (>12 g/dl) were defined as the non-anemic healthy
individuals. Subjects with the history of recent infections
(n=2) and vitamin supplementation (n=2) were excluded
from this study, because these conditions may influence
serum iron parameters and erythropoietic activity.
Subjects were investigated by measurements of hemato-
logic variables, serum iron profiles, and reticulocyte
parameters [i.e., immature reticulocyte fraction (IRF) and
reticulocyte maturity index (RMI)]. The cutoff levels of
sTfR for the subject populations were determined as 1.18
and 3.23 mg/l, which were based on the reference interval
in age-matched adolescents [7]. Subject populations were
categorized as two groups, and the subjects with decreased
sTfR <1.18 mg/l (n=52) were compared to those with
increased sTfR >3.23 mg/l (n=40), especially focused on
IRF, RMI, and iron parameters.
Ann Hematol (2008) 87:571–573
DOI 10.1007/s00277-008-0456-1
Y. H. Jun
Department of Pediatrics, College of Medicine, Inha University,
Incheon, South Korea
C. H. Nahm
:
J. W. Choi
Department of Laboratory Medicine, College of Medicine,
Inha University,
Incheon, South Korea
J. W. Choi (*)
Department of Laboratory Medicine, Inha University Hospital,
7-206, 3-ga, Shinheung-dong, Jung-gu,
Incheon 400-711, South Korea
e-mail: jwchoi@inha.ac.kr