Clinical Information

Iron exists in biological fluids as a component of hemoglobin and myoglobin. It is bound in serum and plasma to transferrin, which acts as a carrier protein. Increased iron concentrations are seen in hemolytic anemias, hemochromatosis, and acute liver disease. Decreased concentrations are seen in iron deficiency and anemia of chronic disease, such as chronic renal disease. Major causes of iron deficiency include gastrointestinal and menstrual bleeding. For assessment of the body’s iron status, the measurement of transferrin and ferritin can provide more accurate information.

Iron is an essential mineral that is needed for the body to function properly. The body does not produce iron, it is absorbed from the foods we eat or from supplements. About 70% of the body’s iron is incorporated into the hemoglobin within red blood cells (RBCs), the remainder is stored in the tissues as ferritin or hemosiderin, with additional small amounts used for other purposes (e.g., to produce other proteins such as myoglobin and some enzymes). Iron is transported throughout the body as Fe(III) bound to the plasma protein apotransferrin. The apotransferrin‑Fe(III) complex is called transferrin.

Iron status is used to diagnosis and management of some hematologic and hepatic conditions. In addition to serum iron levels, several tests may be ordered including unsaturated iron-binding capacity (UIBC), total iron binding capacity (TIBC), iron saturation, and ferritin. Normally about one third of the iron‑binding sites of transferrin are occupied by Fe(III). The remaining transferrin iron-binding sites (those not being used to transport iron) are the unsaturated iron-binding capacity (UIBC). TIBC is a surrogate for transferrin and has a direct relationship to it.

Iron saturation measures the amount of iron bound to transferrin in the blood and indicates how much iron is readily available for use in physiological processes.

UIBC and TIBC are increased in low iron states such as uncomplicated anemia and decreased in high iron conditions such as hemochromatosis. The lone exception to the preceding is the case of anemia of chronic disease where the patient may be anemic but has adequate iron reserves and a low UIBC. Iron saturation is low with iron deficiency and high when there is an excess amount of iron.