Ferritin is an iron-binding globular protein present in every cell type. It is a 450 kDa protein consisting of 24 subunits composed of 2 chains – H & L. ferritin is composed of a protein shell within which about 4500 iron (Fe3+) ions can be stored. Ferritin stores iron so that our body can use it later. It is a buffer against iron deficiency and iron overload is the primary intracellular iron-storage protein in both prokaryotes and eukaryotes, keeping iron in a soluble and non-toxic form.
Ferritin that is not combined with iron is called apoferritin. The amount of ferritin in our blood (serum ferritin level) is directly related to the amount of iron stored in your body. A healthy human adult has a total body iron content of 3599 mg, of which 2000mg is present as circulating hemoglobin, 300 mg is in the form of cell enzymes and pigments. So, the remaining is stored in cells as ferritin or hemosiderin. Hemosiderin is a degraded form of ferritin that has lost part of its protein shell.
Ferritin is present in the blood in very low concentration. Approximately 1% of the plasma iron is contained in ferritin. The plasma ferritin is in equilibrium with body stores and variations in the quantity of iron in the storage compartment are reflected in the plasma ferritin concentration. Expected value of ferritin for females is 10-120 ng/mL and for males is 20-300 ng/mL.
The plasma ferritin concentration declines very early in the development of iron deficiency, long before changes are observed in blood hemoglobin concentration, RBC size or serum iron concentration. Thus, measurement of serum ferritin concentration can serve as a very sensitive indicator of iron deficiency. A ferritin test indirectly measures the amount of iron in our blood. The ferritin levels measured have a direct correlation with the total amount of iron stored in the body including cases of anemia of chronic disease.
If the ferritin level is low, there is a risk for lack of iron, which can lead to anemia. In the setting of anemia, serum ferritin is the most sensitive lab test for iron deficiency anemia. Low ferritin may also indicate hypothyroidism or vitamin C deficiency. Serum Ferritin levels below 10 ng/mL are indicative of iron deficiency anemia.
If ferritin is high there is iron in excess, which will be excreted in the stool. A large number of chronic diseases result in increased serum ferritin concentration which include chronic infections and inflammatory disorders, like renal disease, heart disease, leukemia, rheumatoid arthritis, hemochromatosis, porphyria, pernicious anemia, Hodgkin’s disease, etc. Ferritin level is also elevated during periods of acute malnourishment. Therefore, ferritin can also be used as a marker for iron overload disorders.
Detection:
Serum ferritin levels can assay by any of following methods:
1. ELISA (Enzyme linked Immunosorbent Assay)
2. IRMA (Immuno-radiometric assay-semi automated)
3. Affinity-column-mediated enzyme-linked immuno-sorbent assay
4. Immunocytochemistry
5. ICLA (Immuno chemiluminescent assay)
6. IFMA (Immuno-fluorometric assay)
7. Western blotting
8. Ligand blotting
9. Ferritin-binding Protein Purification (Ferritin can also be detected with the help of ferritin binding proteins e.g. H-Kininogen).