Human Soluble Transferrin Receptor (sTfR) ELISA
Transferrin Receptor (TfR), the major mediator of iron uptake by cells, binds and internalizes diferric transferrin, thereby delivering iron to the cell cytosol. When a cell needs iron, TfR expression is increased to facilitate iron uptake. Since the major use of iron is for hemoglobin synthesis, about 80% of total TfR is on erythroid progenitor cells. Soluble Transferrin Receptor (sTfR) arises from proteolysis of TfR at a specific site in the extracellular domain, leading to monomers that can be measured in plasma. There is a constant relationship between total TfR and the concentration of sTfR in plasma, thus, sTfR in plasma is an indirect measure of total TfR.
Since TfR expression is increased in iron deficiency and since most TfR is on erythroid progenitor cells, the plasma level of sTfR reflects either the erythroid need for iron, or the size of the erythroid progenitor pool (the rate of erythropoiesis). The concentration of sTfR in plasma or serum is elevated in iron deficiency and in subjects with ineffective erythropoiesis or hyperplastic erythropoiesis (hemolytic anemia, b-thalassemia, polycythemia, etc.), and depressed in subjects with hypoplastic erythropoiesis (chronic renal failure, aplastic anemia or post-transplant anemia).
The sTfR assay is a sandwich-type enzyme linked immunosorbent assay (ELISA) for the quantitative determination of soluble transferrin receptor (sTfR) concentrations in human serum and plasma as an aid in the diagnosis of iron-deficiency. The minimum detectable dose of sTfR is typically less than 0.5 nmol/L. The normal sTfR value (at sea level) is 18.4 nmol/L with a range of 8.7 - 28.1 nmol/L. Values among Blacks are higher than those among non-Blacks, and subjects at high altitude (above 1600 m) have higher values than those nearer sea level. The sTfR assay is for in vitro diagnostic use is not intended to be used in isolation; results should be interpreted in conjunction with other diagnostic tests.