A blood test called the Iron and Total Iron Binding Capacity is used to determine the body's iron levels. The total iron binding capacity test evaluates how effectively the iron adheres to transferrin, the protein that aids in transporting the metal throughout the body, as well as to other proteins found in the blood. The human body needs iron for healthy bone marrow, muscles, and organ function, but excessive or inadequate quantities of the mineral can also have serious negative effects on health.