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TIBC (Total iron-binding capacity):
The TIBC measures the total amount of iron that can be bound by proteins in the blood. Since transferrin is the primary iron-binding protein, the TIBC test is a good indirect measurement of transferrin availability.
Transferrin:
is the main protein in the blood that binds to iron and transports it throughout the body. The amount of transferrin that is available to bind to and transport iron is reflected in measurements of the total iron binding capacity (TIBC).
Normally, iron is absorbed from food and transported throughout the body by transferrin, which is produced by the liver. About 70% of the iron is transported to the bone marrow and incorporated into hemoglobin within red blood cells. The remainder is stored in the tissue as ferritin or hemosiderin.
Normal amount of transferrin:
The amount of transferrin in blood depends upon liver function and a person's nutritional status. Under normal conditions, its binding sites are typically about 1/3 saturated with iron. This means that about 2/3 of its capacity is held in reserve
The Test
Total iron-binding capacity (TIBC) is most frequently used along with a serum iron test to evaluate people suspected of having either iron deficiency or iron overload. These two tests are used to calculate the transferrin saturation, a more useful indicator of iron status than just iron or TIBC alone. In healthy people, about 20-40% of available sites in transferrin are used to transport iron.
In iron deficiency, the iron level is low, but the TIBC is increased, thus transferrin saturation becomes very low. In iron overload states, such as hemochromatosis, the iron level will be high and the TIBC will be low or normal, causing the transferrin saturation to increase.
