Iron metabolism - Serum iron: - Transferrin and transferrin saturation - Serum-Ferritin
Iron is present in the body in the ferrous form (Fe++, well-absorbed), as well as in ferric compounds (storage form). Ferric compounds predominate in food. This is why only around 5-10% of oral iron is absorbed. This rate can be increased to a maximum of 30% in iron deficiency. The daily gastrointestinal absorption of iron is normally 1 mg/d. This corresponds rather precisely to the daily loss attained through exfoliation of skin cells, and cells of the gastrointestinal and urogenital tracts. In the case of menstruating women (15-40 mg loss per menstruation) and pregnant women (requirement per pregnancy approximately 500-1000 mg), iron loss is substantially higher. Iron cannot be actively eliminated from the body. For this reason, iron overload can occur under certain circumstances. Iron is stored in the body in the form of ferritin (water-soluble) and hemosiderin (water-insoluble, stainable with Prussian blue).
|Hemoglobin in peripheral blood
(1ml blood = 0.5 mg Fe)
2000 - 2500 mg
|Hemoglobin in bone marrow (erythropoiesis)||
|Remaining functional iron (myoglobin, cytochrome P-450 etc.)||
|Stored iron (ferritin, hemosiderin)||
Total body iron
3500 - 4000 mg
In healthy adults, serum iron is subjected to strong variations. On the other hand, it stabilizes in iron deficiency states at low values and in iron overload at high values. Serum iron is low in both iron deficiency and anemia of chronic disease.
Normal range: - µmol/L
Transferrin and transferrin saturation:
One transferrin molecule binds two iron molecules. Thus, the total iron binding capacity (µmol/L) is twice the value of transferrin (µmol/L). The transferrin saturation represents the percentage of the total iron binding capacity that is used by iron. A value of less than % may be indicative of an iron deficiency.
Normal range for transferrin saturation: - %
Ferritin is a water-soluble complex of apoferritin and ferric hydroxide. The serum ferritin level usually correlates with the available storage iron. A lower value normally suggests depletion of storage iron and therefore iron deficiency. However, a normal value does not exclude iron deficiency. An increased value does not always indicate iron overload, since ferritin can be increased as an acute phase protein in several different states such as liver disease, malignancy and chronic inflammatory processes (see also anemia of chronic disease).
Normal range: men - µg/L, women - µg/L