Iron is used for various physiologic processes, the most important being red blood cell (RBC) production. Transferrin, an iron transport protein that is distributed in plasma and extracellular fluids, binds iron in the plasma (obtained from dietary absorption and iron stores) and transports it to the bone marrow for use in RBC production.

Excess iron not needed for hemoglobin synthesis is processed by the reticuloendothelial system for storage as ferritin, the main iron storage protein.5 Mature RBCs circulate until they are destroyed by phagocytosis and the majority of iron from these RBCs is returned to transferrin; the rest is stored as ferritin.5