The Test Sample
What is being tested?
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), unsaturated iron binding capacity (UIBC), or transferrin saturation.
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 the production of hemoglobin within red blood cells. The remainder is stored in the tissues as ferritin or hemosiderin. The amount of transferrin in the blood depends upon liver function and a person's nutritional status. Under normal conditions, its binding sites are typically one-third saturated with iron. This means that two-thirds of its capacity is held in reserve.
The transferrin test, TIBC, UIBC, and transferrin saturation evaluate the blood's ability to bind and transport iron and are a reflection of iron stores.
- 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.
- The UIBC test determines the reserve capacity of transferrin, i.e., the portion of transferrin that has not yet been saturated with iron. UIBC can be measured directly or calculated as TIBC – iron = UIBC.
- Serum iron measures the total amount of iron in the blood, nearly all of which is bound to transferrin. It is required to calculate either the TIBC or UIBC.
- Transferrin saturation is a calculation (see Common Questions #2) using the iron test result and the TIBC or UIBC results, representing the percentage of the transferrin that is saturated with iron.
How is the sample collected for testing?
A blood sample is drawn by needle from a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
A 12-hour fast may be required. In this case, only water is allowed. A morning specimen is preferred.