Total iron binding capacity (TIBC) - serum iron = unsaturated iron
binding capacity (UIBC). (TIBC - SI = UIBC) TIBC and iron may also be
used to determine "transferrin" saturation. Serum iron divided by TIBC
gives the saturation. UIBC is simply the transferrin in the blood that
does not have iron attached to it. If you have a high saturation you
will generally have a low UIBC. People with uncomplicated iron
deficiency usually have an elevated UIBC. UIBC functions as one of the
major antioxidant activities of blood. Having more of it is generally a
good thing, unless it is reflecting a clinically severe iron
deficiency. Hemochromatosis patients usually have less because of their
high saturation. [INR or international normalized ratio is not an iron
test. It refers to a coagulation parameter and is often followed in
persons taking anticoagulants.]

Jerome L. Sullivan, MD, PhD