Revisiting Iron Metabolism, Iron Homeostasis and Iron Deficiency Anemia

Background: Iron deficiency anemia (IDA) is one of the commonest clinical scenarios especially in children, women of childbearing age, and elders. The crux of this review was revisiting iron homeostasis, mechanism of iron absorption, causes, laboratory diagnosis, and management of IDA. Methods: This narrative review is compiled after a relevant literature search from electronic databases including, but not limited to, Google, Google Scholar, PMC, PubMed, Science Direct, and Scopus. The key words used for searching relevant literature include iron, iron deficiency, iron deficiency anemia, iron metabolism, hepcidin, transferrin, causes of iron deficiency anemia, and laboratory diagnosis of iron deficiency anemia. Reference hematology books were also consulted. Results: According to the published literature, about one mg of iron is required daily which equals its loss, although the iron requirement increases in pregnancy and lactating mothers. Dietary non heme iron (oxidized Fe3+) is reduced to the ferrous (Fe2+) form by ferrireductase present in the brush border of duodenal enterocytes. Ferrous iron is absorbed in the brush border of duodenal enterocytes through a carrier protein, divalent metal transporter 1 (DMT1). Heme iron is absorbed by the duodenal enterocytes through a mechanism that is not well understood or a receptor yet to be discovered. Transferrin receptor helps in the internalization of iron in the cells. Hepcidin acts as a gatekeeper and controls iron absorption by enterocytes and macrophages. IDA may be caused by decreased intake of iron, increased iron requirements or loss of iron from the body. Conclusions: Iron deficiency anemia is the most common nutritional anemia that affects large numbers of people in developed as well as in developing countries. It is estimated that approximately 2 billion people around the world have IDA. Microcytosis with marked reduction in serum iron, decreased % saturation of transferrin, low ferritin, and reduced or even undetectable hepcidin are the laboratory features of IDA. In addition, total iron binding capacity and soluble transferrin receptors increase significantly in IDA. Management of IDA is incomplete if the underlying cause is not ruled out and left untreated.