Ferritin is a globular protein found mainly in the liver, which can store about 2’250 iron (Fe3+) ions. The ferritin molecule consists of a protein shell (apoferritin) composed of heavy and light subunits, which surrounds a crystalline core containing iron oxide and phosphate. It is synthesised in the liver, spleen and numerous other body tissues, with major concentrations found in the liver, spleen, bone marrow and intestinal mucosa.
Ferritin levels have a direct correlation with the total amount of iron stored in the body. If ferritin is high there is iron in excess, which would be excreted in the stool. If ferritin levels are low there is a risk for lack of iron, which sooner or later could lead to anaemia.
In the setting of anaemia, serum ferritin is the most sensitive lab test for iron deficiency anaemia. In contrast, serum ferritin levels are normal or increased in anemia associated with chronic disease. Elevated serum ferritin levels have been observed in acute and chronic liver disease and lymphoid malignancy (leukemia and Hodgkin lymphoma). High serum ferritin levels have also been associated with an elevated risk for myocardial infarction in men. Ferritin is also used as a marker for iron overload disorders, such as haemochromatosis in which the ferritin level may be abnormally raised.
Ferritin is an acute-phase reactant and is often elevated in the course of disease. Free iron is toxic to cells and the body has an elaborate set of protective mechanisms to bind iron in various tissue compartments. Within cells, iron is stored complexed to protein as ferritin or hemosiderin. Apoferritin binds to free ferrous iron and stores it in the ferric state. Under steady state conditions, the serum ferritin level correlates with total body iron stores; thus, serum ferritin level is the most convenient laboratory test to estimate iron stores.