At a Glance
Why Get Tested?
To assess your body's ability to transport iron in the blood
When to Get Tested?
When your doctor suspects you may have too much or too little iron in your body because of a variety of conditions; to help monitor liver function and nutrition
A blood sample drawn from a vein in your arm
Test Preparation Needed?
You may be instructed to fast for 12 hours before the test; in this case, only water is allowed.
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.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
Gersten, T. (Updated 2012 February 8). Total iron binding capacity. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003489.htm. Accessed April 2013.
(© 1995-2013). Iron and Total Iron-Binding Capacity, Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/34624 through http://www.mayomedicallaboratories.com. Accessed April 2013.
Devkota, B. (Updated October 4). Iron-Binding Capacity. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2085726-overview through http://emedicine.medscape.com. Accessed April 2013.
(Update 2013 March). Hemochromatosis. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/Hemochromatosis.html?client_ID=LTD#tabs=6 through http://www.arupconsult.com. Accessed April 2013.
Yamanishi, H. et. al. (2003 January). Total Iron-binding Capacity Calculated from Serum Transferrin Concentration or Serum Iron Concentration and Unsaturated Iron-binding Capacity. Clinical Chemistry v 49 (1) 175-178 [On-line information]. Available online at http://www.clinchem.org/content/49/1/175.full through http://www.clinchem.org. Accessed April 2013.
S6 Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 594-598.
Sources Used in Previous Reviews
Corbett, JV. Laboratory Tests & Diagnostic Procedures with Nursing Diagnoses, 4th ed. Stamford, Conn.: Appleton & Lang, 1996. Pp. 34-35, 41-43.
Frey, Rebecca J. Iron Tests. Chapter in: Gale Encyclopedia of Medicine, Edition One, 1999 Gale Research Group, Pg. 1648.
Witte DL, Crosby WH, Edwards CQ, Fairbanks VG, Mitros FA. Practice guideline development task force of the College of American Pathologists.
Boston University Medical Center. Community Outreach Health Information System. Available online at http://www.bu.edu/cohis/cardvasc/blood/anemia.htm#prevent through http://www.bu.edu.
Lyon, Elaine and Frank, Elizabeth L. Hereditary Hemochromatosis Since Discovery of the HFE Gene. Clinical Chemistry 47:1147-1156 (Jul 2001).
Pagana, K. D. & Pagana, T. J. (© 2007). Mosby's Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 574-577.
Clarke, W. and Dufour, D. R., Editors (© 2006). Contemporary Practice in Clinical Chemistry: AACC Press, Washington, DC. Pp 43, 200-201.
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 1062-1065.
Dugdale III, D. (Updated 2009 February 13). Total Iron Binding Capacity. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003489.htm. Accessed June 2009.
(Modified 2009 March 13). About Iron. Iron Disorders Institute [On-line information]. Available online at http://www.irondisorders.org/Disorders/about.asp through http://www.irondisorders.org. Accessed June 2009.
(Updated 2007 August 24). Dietary Supplement Fact Sheet: Iron. NIH Office of Dietary Supplements [On-line information]. Available online at http://ods.od.nih.gov/factsheets/iron.asp through http://ods.od.nih.gov. Accessed June 2009.
Rathz, D. et. al. (Updated 2009 February 02). Toxicity, Iron. eMedicine [On-line information]. Available online at http://emedicine.medscape.com/article/166933-overview through http://emedicine.medscape.com. Accessed June 2009.
Chen, Y. (Updated 2009 April 05). Iron Deficiency Anemia. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000584.htm. Accessed June 2009.
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