The index of transferrin present in circulating blood is the iron-binding capacity. Transferrin can be nearly one third saturated with iron. The unsaturated iron-binding capacity (UIBC) is measured using radioactive iron or spectrophotometric approaches. The sum of the UIBC and the plasma iron is the total iron-binding capacity (TIBC).
Direct measurement of the TIBC may also be performed.
The iron-binding capacity reference range is 255-450 μg/dL.