Unsaturated iron binding capacity (UIBC) may also be used as a marker for altered iron metabolism. UIBC represents the portion of iron binding sites on transferrin that are not occupied by iron. Therefore, a low UIBC indicates that transferrin is highly saturated with iron, a finding consistent with hereditary hemochromatosis (HH). HH may be suspected when the UIBC is less than 143 micrograms/dL, a criterion suggested by the results of one study.(5)

UIBC may be a lower cost alternative to the more complex transferrin saturation (TS). UIBC and SI are both fully automated procedures that are available on widely used laboratory instruments.

The TIBC can be calculated by adding UIBC and SI, resulting in a value for TIBC that can be used for determining TS:

TS = SI/(SI + UIBC) X 100