Total iron-binding capacity is a medical test to determine the availability of an iron binding protein, transferrin, in blood, by measuring transferrin in plasma, which contains free transferrin produced by the liver. It is usually performed with other tests when iron deficiency or anemia is suspected.
The normal level of iron-binding capacity is 250-307 micrograms of iron for every decilitre of blood. Depending on the results of other tests, high levels can indicate iron deficiency anemia (as the liver produces transferrin to utilize all available iron). However, a high result in a pregnant woman or a woman taking the contraceptive pill is normal. Low levels point to other forms of anemia, usually secondary to another condition.