Soluble Transferrin Receptor (sTfR), plasma or serum

Transferrin receptor (TfR) is a cell membrane glycoprotein with a molecular mass of 190 kDa. Cellular iron uptake is mediated by TfR. TfR binds plasma diferric transferrin and internalizes the TfR-transferrin complex, where transferrin provides its iron to the cytosol. The receptor-bound transferrin recycles to the cell surface and is able to bind another diferric transferrin. The prime determinants of sTfR concentration are cellular iron requirements and the erythrocyte proliferation rate. The measurement of sTfR has been introduced as a powerful tool for the diagnosis of iron deficiency in a variety of clinical situations. Basically, the concentration of serum sTfR increases in iron deficiency anemia and in conditions of high turnover erythropoiesis (i.e. hemolytic anemia). Decreased concentrations of sTfR have been detected in aplastic anemia and chronic renal failure.The sTfR concentration has also been shown to be a more  sensitive and less variable index of iron status than the more conventional serum iron, transferrin and total iron-binding capacity