Total iron-binding capacity

Total iron-binding capacity is a medical laboratory test which measures the extent to which iron-binding sites in the serum can be saturated. Of the large amount of iron that is stored in the body, only a small fraction is actually transported in the serum. The protein that does this transporting of iron around the body is called transferrin. A single molecule of transferrin can carry 2 molecules of iron, and in a normal person, only about 30% of these spots for iron are filled. Generally speaking, if the iron stores in the body are low, fewer of these spots on the transferrin molecules will be filled by iron, and the TIBC will therefore be higher.

Taken together with serum iron and percent transferrin saturation clinicians usually perform this test when they are concerned about anemia, iron deficiency or iron deficiency anemia. However, because the liver produces transferrin, liver function must be considered when performing this test. It can also be an indirect test of liver function, but is rarely used for this purpose.

The liver produces more transferrin in response to iron deficiency, so the percent transferrin saturation (i.e., the result of the formula of serum iron/TIBC x 100) can also be a useful indicator.

In simple iron deficiency anemia, the serum iron is low, the transferrin is high, and therefore the percent transferrin saturation is very low.

On the other hand, in anemia of chronic disease, the body holds iron out of the serum but also produces less transferrin (presumably as part of a response to keep iron away from pathogens that require it for their metabolism). In this case, serum iron is low but the TIBC (that is, the transferrin) is low. So the percent transferrin saturation is normal.

In women who are pregnant or are using hormonal contraception, the liver increases the production of transferrin. This produces a higher TIBC and a lower percent transferrin saturation even with normal iron.

These examples demonstrate that to properly understand a value for TIBC, one also must know the serum iron, the percent transferrin saturation, and the individual clinical situation.

To do the test, labs use serum from blood drawn from a vein.

Usual values

* Serum iron: Male 65-177 μg/dL (11.6-31.7 μmol/L)
* Serum iron: Female 50-170 μg/dL (9.0-30.4 μmol/L)
* TIBC: 240-450 μg/dL (43.0-80.6 μmol/L)
* Transferrin saturation: Male 20-50%
* Transferrin saturation: Female 15-50%

μg/dL = micrograms per deciliter; μmol/L = micromoles per litre.

Laboratories often use different units and "normal" may vary by population and the lab techniques used. Look at the individual laboratory reference values to interpret a specific test (for instance, your own).