Iron transport in the plasma is carried out by transferrin, which gives iron to cells through its interaction with a specific membrane receptor, the transferrin receptor (TfR).
\nIron uptake into cells is mediated through internalizing iron-transferrin complexes. The iron-transferrin complex binds to transferrin receptors exposed on the outer side of the plasma membrane and is internalized through endosomes with the ultimate release of iron into the cytoplasm.
\nA soluble form of the TfR (sTfR) has been identified in serum.
\nsTfR is a truncated monomer (70 kDa) of the tissue receptor, lacking its first 100 amino acids, which retains its transferrin binding activity. sTfR circulates as a complex of transferrin and its receptor.
\nThe erythroblasts rather than reticulocytes are the primary source of serum sTfR.
\nThe concentration of sTfR is an indicator of iron status.
\nIron deficiency causes overexpression of transferrin receptor, and sTfR levels, while iron repletion results in decreased sTfR levels.
\nBlood testing of the soluble transferrin receptor (sTfR) is used as a measure of functional iron status, and for the investigation of iron deficiency anaemia.
\nAlthough ferritin measurement is the accepted method for assessing iron deficiency, it is an acute-phase reactant and increases in response to processes that do not correlate with iron status, including inflammation, chronic disease, malignancy, and infection.
\nsTfR is not an acute-phase reactant, and the interpretation of iron status using sTfR measurement is not affected by these confounding pathologies.
\nThe test is useful for evaluating suspected iron deficiency in patients who may have inflammation, infection, or chronic disease and other conditions in which ferritin concentration does not correlate with iron status (1).<\/p>\n
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