Ferritin is a globular protein complex of 450 kDa consisting of 24 protein subunits and is the 
primary intracellular iron-storage protein in both prokaryotes and eukaryotes, keeping iron in a soluble and non-toxic form. It occurs normally in almost all tissues of the body but especially in hepatocytes and reticuloendothelial cells, where it serves as iron reserve. Ferritin is aslo present in the serum in minute amounts, where it appears to reflect iron stores in normal individuals.

A low serum ferritin value is thought to be the best laboratory indicator of iron depletion. Virtually all patients with low serum iron and low ferritin have iron deficiency. Serum ferritin is clincially useful in distinguishing between iron-deficiency anemia(serum ferritin diminished levels) and “anemia of chronic disease”(serum ferritin levels usually normal or elevated). Serum ferritin is a good screening test in separating erythrocytes microcytosis due to iron deficiency(low values) from microcytosis related to thalassemia minor(normal or high values). An iron-depletion state with a decreased serum ferritin value is quite common among menstruating and reproductively active females and in children.

A high serum ferritin value is seen in hemochromatosis and other iron-overload states, as well as cute hepatitis, Gaucher disease, malignancies, and chronic inflammatory disorders.