Ferritin is a complex formed by deferrin and trivalent iron ions, the core of ferric ion globulin, which has a strong capacity to bind iron and reserve iron to maintain the body’s iron supply and the relative stability of hemoglobin. An increase in ferritin alone is often clinically significant. Increased ferritin can be seen in primary hemochromatosis or secondary iron overload, and is especially common in patients with long-term blood transfusions. Ferritin may also be significantly increased in the presence of acute inflammatory and neoplastic diseases, as well as in leukemia and hyperthyroidism. Certain anemic diseases, such as hemolytic anemia, aplastic anemia, and pernicious anemia, also show a significant increase in ferritin. Also, there is a rare hematologic disorder called hemophagocytic syndrome in which ferritin can be significantly increased. Ferritin greater than 500ug/L is one of the conditions for the diagnosis of hemophagocytic syndrome.