Transferrin and Iron-binding Capacity (TIBC, UIBC)
- Also Known As:
- Iron Binding Capacity
- IBC
- Serum Iron-Binding Capacity
- Siderophilin
- TIBC
- UIBC
- Formal Name:
- Transferrin
- Total Iron Binding Capacity
- Unsaturated Iron Binding Capacity
- Transferrin Saturation
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At a Glance
Why Get Tested?
Along with other iron tests, to assess your body’s ability to transport iron in the blood; to help diagnose iron-deficiency or iron overload
When To Get Tested?
When you have low hemoglobin and hematocrit on a complete blood count (CBC); when your healthcare practitioner suspects you may have too much iron (overload) or too little iron (deficiency) in the body
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
You may be instructed to have your blood drawn in the morning and/or fast for 12 hours before the test; in this case, only water is allowed. Follow any instructions from your healthcare practitioner and/or from the laboratory performing the test.
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You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.
Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.
The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.
If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.
Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.
While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”
For more information, please read the article Reference Ranges and What They Mean.
What is being tested?
Transferrin is the main protein in the blood that binds to iron and transports it throughout the body. A transferrin test directly measures the level in the blood. Alternatively, transferrin may be measured indirectly (or converted by calculation) so that its level is expressed as the amount of iron it is capable of binding. This is called the total iron binding capacity (TIBC).
Iron is an essential nutrient that, among other functions, is necessary for the production of healthy red blood cells (RBCs). It is a critical part of hemoglobin, the protein in RBCs that binds oxygen in the lungs and releases oxygen as blood circulates to other parts of the body. The body cannot produce iron and must absorb it from the foods we eat or from supplements.
Normally, iron is transported throughout the body by transferrin, which is produced by the liver. In healthy people, most iron is incorporated into the hemoglobin within RBCs. The remainder is stored in the tissues as ferritin or hemosiderin, with additional small amounts used for other purposes (e.g., to produce other proteins such as myoglobin and some enzymes).
The transferrin test, TIBC, UIBC, and transferrin saturation, along with other iron tests, help evaluate the amount of iron in the body by measuring several substances in the blood. These tests are often ordered at the same time and the results interpreted together to help diagnose and/or monitor iron deficiency or iron overload.
- Serum iron test—measures the total amount of iron in the liquid portion of the blood, nearly all of which is bound to transferrin.
- Transferrin test—directly measures the level of transferrin in the blood. The level depends upon liver function and a person’s nutritional status. Transferrin is a protein that may decrease during any inflammatory process and is referred to as a negative acute phase reactant.
- TIBC (total iron-binding capacity)—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 amount of transferrin that is available to bind to iron. (Note: Though TIBC is a reflection of the amount of transferrin available, TIBC and transferrin are not synonymous.)
- UIBC (unsaturated iron-binding capacity)—this test determines the reserve capacity of transferrin, i.e., the portion of transferrin that has not yet been saturated with iron.
- Transferrin saturation— dividing the iron concentration by the TIBC produces an estimate of how many of transferrin iron-binding sites are occupied; this is called the transferrin saturation. Under normal conditions, transferrin is typically one-third saturated with iron. This means that about two-thirds of its capacity is held in reserve. (Less commonly, the iron concentration may be divided by the transferrin concentration, not the TIBC. This similar estimate is usually called the transferrin index.)
- Ferritin—measures the level of ferritin, a protein made by almost all cells in response to increased iron. The ferritin level reflects the total body iron. It will be low when there is iron deficiency and high when there is an excess of iron in the body.
When the level of iron is insufficient to meet the body’s needs, the level of iron in the blood drops and iron stores are depleted. This may occur because:
- There is an increased need for iron, for example during pregnancy or childhood, or due to a condition that causes chronic blood loss (e.g., peptic ulcer, colon cancer)
- Not enough iron is consumed (either foods or supplements)
- The body is unable to absorb iron from the foods eaten in conditions such as celiac disease
Insufficient levels of circulating and stored iron may eventually lead to iron deficiency anemia (decreased hemoglobin and hematocrit, smaller and paler red cells). In the early stage of iron deficiency, no physical effects are usually seen and the amount of iron stored may be significantly depleted before any signs or symptoms of iron deficiency develop. If a person is otherwise healthy and anemia develops over a long period of time, symptoms may not appear before the hemoglobin in the blood drops below the lower limit of normal.
However, as the iron deficiency progresses, symptoms eventually begin to appear. The most common symptoms of anemia include fatigue, weakness, dizziness, headaches and pale skin. Read the article on Anemia to learn more.
Conversely, too much iron can be toxic to the body. Iron storage and ferritin levels increase when more iron is absorbed than the body needs. Absorbing too much iron over time can lead to the progressive buildup of iron compounds in organs and may eventually cause their dysfunction and failure. An example of this is hemochromatosis, a rare genetic disease in which the body absorbs and builds up too much iron, even on a normal diet. Additionally, iron overload can occur when a person undergoes repeated blood transfusions.
Common Questions
Health Professionals – LOINC
LOINC Observation Identifiers Names and Codes (LOINC®) is the international standard for identifying health measurements, observations, and documents. It provides a common language to unambiguously identify things you can measure or observe that enables the exchange and aggregation of clinical results for care delivery, outcomes management, and research. Learn More.
Listed in the table below are the LOINC with links to the LOINC detail pages. Please note when you click on the hyperlinked code, you are leaving Lab Tests Online and accessing Loinc.org.
| LOINC | LOINC Display Name |
|---|---|
| 3034-6 | Transferrin [Mass/Vol] |
| 22674-6 | Transferrin [Moles/Vol] |
| 2501-5 | Iron binding capacity.unsaturated [Mass/Vol] |
| 22753-8 | Iron binding capacity.unsaturated [Moles/Vol] |
| 2500-7 | Iron binding capacity [Mass/Vol] |
| 14800-7 | Iron binding capacity [Moles/Vol] |
| 2505-6 | Iron/Iron binding capacity.total [Mass ratio] |
| 39778-6 | Iron/Iron binding capacity.total [Molar ratio] |
| 2502-3 | Iron saturation [Mass fraction] |
| 14801-5 | Iron saturation [Molar fraction] |
View Sources
Sources Used in Current Review
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Harper, J. and Conrad, M. (2015 November 7 Updated). Iron Deficiency Anemia. Medscape Drugs and Diseases. Available online at http://emedicine.medscape.com/article/202333-overview. Accessed on May 2017.
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Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Nader Rifai. 6th edition, Elsevier Health Sciences; 2017. Pg 742.
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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.
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