Sideremia and total iron binding capacity (TIBC): calculation, formula, transferrin values

By Cristiano Antonino On Mar 25, 2023

TIBC (acronym from the English Total Iron Binding Capacity) is a parameter, detectable by a simple venous blood test, that indicates how well plasma proteins (particularly transferrin) are able to bind oxidised iron (Fe3+) and transport it into the circulatory stream

Remember that in the blood, transferrin can be found

in free form (unsaturated transferrin, not bound to iron);
in an iron-bound form (saturated, iron-bound transferrin).

The amount of bound transferrin coincides with the sideremia value.

The amount of transferrin available for iron binding and transport is reflected in the measure of total iron-binding capacity (TIBC), latent iron-binding capacity or transferrin saturation.

Since TIBC is an indirect measure of transferrin’s ability to bind iron, although transferrinemia and TIBC are two different tests, they have overlapping trends and essentially the same clinical significance.

TIBC calculation

This is a calculation for which it is necessary to determine the serum iron concentration (normal values: men: 12-25 µmol/L – women: 11-22 µmol/L) and transferrinemia.

Why is it useful to know the TIBC?

Determination of total iron-binding capacity is prescribed when abnormalities in iron metabolism are suspected.

In clinical practice, TIBC is generally assessed together with

ferritinemia: the concentration of ferritin, the main protein involved in iron storage;
transferrinemia: the concentration of transferrin, the main iron transport protein in the blood;
sideremia: the proportion of circulating transferrin that is saturated with iron.

Normal TIBC values and sideremia/TIBC ratio

Normal values of total iron-binding capacity vary between: 240 and 450 μg/dL (43.0 – 80.6 μmol/L).

The ratio of sideremia to TIBC defines transferrin saturation, a figure usually expressed as a percentage.

Transferrin saturation = (sideremia/TIBC) x 100

Normal values men: 20-50%

Normal values for women: 15-50%.

Altered TIBC values

In a situation of iron deficiency, the body will do its best to take up as much iron as possible, transferrin will be less saturated, and the total iron-binding capacity will consequently be greater; conversely, in a situation where there is plenty of iron in the body (overload), TIBC will decrease so as not to encourage this overload.