Iron is a structural part of hemoglobin, which functions to transport oxygen. Ingested iron is mainly absorbed in the form of Fe2 + in the duodenum and upper jejunum. Absorbed iron is then transported in blood plasma by transferrin-iron complexes. A maximum of 2 Fe2 + ions per transferrin molecule can be transported. Serum iron is almost completely bound to transferrin.
Testing for iron (non-heme) levels is used in the diagnosis and treatment of diseases such as iron deficiency anemia and hemochromatosis. Hemochromatosis is a disease associated with iron deposits in tissues, usually deposited in the form of iron-containing pigments such as hemosiderin and hemofuscin. Disease is characterized by pigmentation of the skin and chronic renal disease. In addition, iron testing can be useful in the diagnosis and monitoring of microcytic anemias (e.g. due to iron metabolism disorders and hemoglobinopathies), macrocytic anemias (e.g. due to vitamin B12 deficiency, folic acid deficiency, and drug-induced metabolic disorders of unknown origin), normocytic anemias such as anemia of chronic renal disease (erythropoetin deficiency), hemolytic anemia, bone marrow disease, and toxic bone marrow damage. Percent iron saturation should also be obtained because it is more helpful than serum iron in estimating iron stores and evaluating for iron deficiency anemia.