Total Iron Binding Capacity

A total iron-binding capacity test is a blood test that tells you how much transferrin in your blood is binding to iron, which tells you how well iron is functioning in your body.

The liver makes a protein called transferrin that attaches to, or binds to, iron in your blood. Once iron is bound to transferrin, it goes to your bone marrow to make red blood cells and hemoglobin, a protein that helps carry oxygen.

Unsaturated iron-binding capacity (UIBC). This measures how much transferrin is not yet bound to iron.

Total iron-binding capacity (TIBC). This is the total amount of iron in your blood plus the UIBC.