No fasting required.

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. 

Your 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.