Clinical Information

Transferrin is the primary plasma iron transport protein, which binds iron strongly at physiological pH. It is a glycoprotein with an approximate molecular weight of 80 kDa, consisting of a polypeptide strand with two N-glycosidically linked oligosaccharide chains with two homologous binding sites for ferric (Fe 3+) iron serving to keep iron nonreactive in circulation and deliver it to cells with transferrin receptors.

The rate of transferrin synthesis in the liver can be altered according to the body's iron requirements and iron reserves. The circulating concentration increases in response to iron deficiency and decreases in response to iron overload. Transferrin concentration also depends on liver function and nutritional status. It also acts as a negative acute phase reactant, decreasing in concentration in the presence of inflammation; however, it has a minor intraindividual biologic variation of 5%. Transferrin is generally only 25% to 30% saturated with iron. Total iron binding capacity (TIBC) can be estimated from transferrin concentration using the molecular weight of the transferrin and accounting that 1 transferrin molecule can bind 2 atoms of iron.(1)

The degree of iron saturation is a more useful indicator of functional iron depletion or overload than transferrin concentration alone. Serum iron, TIBC, and percent saturation are widely used for the diagnosis of iron deficiency and hemochromatosis. However, serum ferritin is a much more sensitive and reliable test for demonstration of iron deficiency. Soluble transferrin receptor performs similarly and is unaffected by inflammation. Reticulocyte hemoglobin has also been used as a sensitive early indicator of iron deficiency and anemia.