CIRCULATING TRANSFERRIN RECEPTORS AND ASSESSMENT OF IRON STATUS

A soluble form of the transferrin receptor is uniformly detectable in human sera. Biochemical studies have shown that this soluble material consists of the extracellular domain of the intact receptor with a truncation site between arginine (100) and leucine (101). Cell biologic models have demonstrated that the serum receptor is produced by proteolytic cleavage at the surface of the exosome within the multivesicular endosome. The cleavage is produced by a membrane-associated serine protease at a site distinct from that produced by trypsin. Clinical studies have demonstrated that the serum transferrin receptor concentration correlates with the number of red cell precursors in the bone marrow in various hematologic disorders and with the deficit in functional iron in patients with iron deficiency. The latter finding has led to a significant refinement in the assessment of iron status. By employing the serum ferritin determination as a measure of body iron stores and the serum transferrin receptor as an index of tissue iron deficiency, it is possible to evaluate the entire spectrum of body iron status. Measurement of the serum transferrin receptor has been particularly useful in detecting iron deficiency in pregnancy and in distinguishing iron deficiency anemia from the anemia of chronic disease.