A blood test for total iron binding capacity is usually done along with a test to check serum iron level. Doctors usually order these two tests in people that have a low red blood cell count. This is also called anemia.

The combination of the two tests can help determine if Iron deficiency is the cause of the anemia. People with iron deficiency anemia have a low serum iron level and a high total iron binding capacity.

The two tests also are used to find out if a person might have an iron overload. This is called hemochromatosis. People with too much iron have a slightly low total iron binding capacity and a high serum iron level.

Sometimes both the total iron binding capacity and serum iron levels are below normal. When this occurs, other causes of the low iron binding capacity need to be considered.

A protein called transferrin, which is made in the liver, does most iron binding in the blood. If the level of this protein falls, the person will have a low total iron binding capacity.

Low levels of transferrin (and therefore a low total iron binding capacity) can be caused by:

• Persistent active diseases such as rheumatoid arthritis and certain cancers
• Malnutrition
• Cirrhosis

When a person has a low red blood cell count, a low serum iron level and a low total iron binding capacity, doctors call this "anemia of chronic disease."