% Saturation of Transferrin
The main utility of measuring TIBC in addition to serum iron is to calculate the percent
saturation of transferrin:
% saturation of Tf = [serum iron divided by TIBC] x 100
In health, roughly 33% of
the circulating iron binding sites are occupied (range: 20-50%). The percent saturation of transferrin
tends to be a more useful parameter clinically than the serum iron alone.
Changes in % saturation with disease
- Iron deficiency - if not complicated by concurrent inflammatory disease, TIBC tends to be
high normal to normal. Coupled with the expected low serum iron, this results in a low
% sat. Tf (generally less than 15%, often much lower). The best way to confirm iron deficiency is to demonstrate lack of iron stores in marrow in species that normally contain bone marrow iron (all species, except for cats).
- Iron overload - The opposite occurs in conditions associated with excessive iron. TIBC tends
to decrease while serum iron is high, resulting in a high % sat. Tf.
- Hemolytic anemia - High serum iron (increased turnover and absorption) results in a high %
- Inflammatory or neoplastic (chronic) disease - These conditions can result in
decreased Tf synthesis and decreased serum levels of Tf. This phenomenon usually results in a decreased serum iron and TIBC (so % saturation is unaffected). However, in many cases of chronic or inflammatory disease, TIBC levels are unaltered and serum iron and percentage saturation values mimic iron deficiency.