Ferritin is a ubiquitous iron storage protein with a nanometer-sized hydrated iron oxide core and a cage-like protein shell. Ferritin is a protein containing 20% iron. Normally, it exists in almost all body tissues, especially hepatocytes and reticuloendothelial cells, as an iron store. Trace amounts of serum ferritin reflect normal iron stores. Detection of serum ferritin is an important basis for the diagnosis of iron deficiency anemia.