Ferritin is the body's major iron-storage protein and its levels in serum are parallel to iron stores. Normally, 1 ng/mL of serum ferritin is related to about 8 mg of iron in storage. It rises somewhat in males and post-menopausal females. Any rise or decrease in levels of serum ferritin indicates available iron stores in the body.
As a diagnostic tool, serum ferritin is the most sensitive test of iron-deficiency anemia in a patient. In presence of iron deficiency, ferritin is generally the first sign followed by decreased iron levels and changes noted in red blood cells such as size, color and number. Low levels of ferritin indicate reduced iron stores or, rarely, malnutrition due to protein depletion. A decrease can also result from hemodialysis. Levels below 10 mg/100 mL is a diagnosis of iron-deficiency anemia.
Higher levels, in contrast, indicate hemochromatosis, hemosiderosis, iron poisoning, or a recent blood transfusion. A higher level of ferritin can also be found in patients with megaloblastic anemia, hemolytic anemia and chronic hepatitis. It is also elevated in those with chronic disease states such as chronic liver disease, uremia, alcoholism, collagen diseases or neoplasm.
The serum ferritin study is limited because ferritin may act as an acute-phase reactant protein such as in states of inflammatory diseases, infections, metastatic cancer and lymphomas. In these cases, ferritin levels may increase one or two days after onset and peak at three to five days. To classify anemias, tests of serum ferritin should be accompanied with serum iron levels and total iron-binding capacity.
There are also interfering factors with serum ferritin, mainly blood transfusions, recent dietary intake of red meat, hemolytic diseases, iron storage disorders like hemochromatosis, menstruation (women will have decreased ferritin levels after menstruation), and drugs that increase ferritin levels.
Pagana, K.D., Pagana, T.J. Mosby's Manual of Diagnostic and Laboratory Tests, 3rd ed. Mosby Elsvier, 2006, pp 249-50.