Ferritin is the iron storage protein. It has a molecular weight of ≥ 440000 daltons, depending upon the iron content, and consists of a protein shell (apoferritin) of 24 subunits and an iron core containing an average of approx. 2500 Fe 3+ ‑ions (in the basic isoforms). Common to all isoforms is their construction from two separate subunits, the acidic H (heavy)‑type subunit and the weakly basic L (light)‑type subunit. The basic isoferritins are responsible for the long‑term iron storage function and are mainly detectable in the liver, spleen and bone marrow. Acid isoferritins are found mainly in the myocardium, placenta, tumor tissue and - to a lesser extent - in the depot organs.
The determination of ferritin is necessary above all in iron metabolism diagnosis, monitoring iron therapy, ascertaining the iron reserves in groups at risk and in the differential diagnosis of anemias. It encompasses prelatent and latent iron deficiency as well as iron overloading. It is also used to distinguish between hypoferric anemia and hypochromic anemia (chronic infection and tumor anemias, sideroblastic anemia or thalassemia).
Ferritin determinations are particularly suitable for monitoring renal anemia when iron utilization and distribution disorders are present during therapy with erythropoietin. The ferritin detectable in blood is in equilibrium with the body’s depot iron and hence acts as an indicator for the level of the iron stores.