Ingested iron is mainly absorbed in the form of Fe 2+ in the duodenum and upper jejunum. The trivalent form and the heme‑bound Fe 3+ component of iron in food has to be reduced by vitamin C. About 1 mg of iron is assimilated daily. Upon reaching the mucosal cells, Fe 2+ ions become bound to transport substances. Before passing into the plasma, these are oxidized by ceruloplasmin to Fe 3+ and bound to transferrin in this form. The transport of Fe ions in blood plasma takes place via transferrin‑iron complexes. A maximum of 2 Fe 3+ ions per protein molecule can be transported. Serum iron is almost completely bound to transferrin.
Iron (non‑heme) measurements are used in the diagnosis and treatment of diseases such as iron deficiency anemia, hemochromatosis (a disease associated with widespread deposit in the tissue of the two iron‑containing pigments, hemosiderin and hemofuscin, and characterized by pigmentation of the skin), and chronic renal disease. Iron determinations are performed for the diagnosis and monitoring of microcytic anemia (e.g. due to iron metabolism disorders and hemoglobinopathy), macrocytic anemia (e.g. due to vitamin B12‑deficiency, folic acid deficiency and drug‑induced metabolic disorders of unknown origin) as well as normocytic anemias such as renal anemia (erythropoetin deficiency), hemolytic anemia, hemoglobinopathy, bone marrow disease and toxic bone marrow damage.