Also Known As
Iron Binding Capacity
Serum Iron-Binding Capacity
Formal Name
Total Iron Binding Capacity; Unsaturated Iron Binding Capacity; Transferrin; Transferrin Saturation
This article was last reviewed on
This article waslast modified on
March 18, 2018.
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

Sample Required?

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.

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. 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.

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.

Accordion Title
Common Questions
  • How is it used?

    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 transferrin sites 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. UIBC may be ordered as an alternative to TIBC.

    It is customary to test for transferrin (instead of TIBC or UIBC) when evaluating a person's nutritional status or liver function. Because it is made in the liver, transferrin will be low in those with liver disease. Transferrin levels also drop when there is not enough protein in the diet, so this test can be used to monitor nutrition.

  • When is it ordered?

    TIBC or UIBC may be ordered along with serum iron when it appears that a person has iron deficiency or overload. One or more tests may be ordered when there are signs of anemia, especially when a CBC is performed and shows red blood cells that are microcytic and hypochromic and the hemoglobin and hematocrit levels are low.

    The most common symptoms of anemia include:

    • Chronic fatigue/tiredness
    • Dizziness
    • Weakness
    • Headaches
    • Pale skin (pallor)

    When a doctor suspects that a person may have iron overload or when a person has a family history of hemochromatosis, iron and TIBC may be ordered along with a ferritin test. Symptoms of iron overload will vary from person to person and tend to worsen over time. They are due to iron accumulation in the blood and tissues. Symptoms may include:

    However, many people have no initial symptoms.

    Iron and TIBC are also ordered when there is a case of suspected iron poisoning. This is most common in children who accidentally overdose with vitamins or other supplements containing iron.

    A transferrin test may be ordered along with other tests such as prealbumin when a doctor wants to evaluate or monitor a person's nutritional status.

  • What does the test result mean?

    The results of transferrin tests, TIBC, or UIBC are usually evaluated in conjunction with other iron tests. A summary of the changes in iron tests seen in various diseases of iron status is shown in the table below.

    Disease Iron TIBC/Transferrin UIBC



    Iron Deficiency Low High High Low Low
    Hemochromatosis High Low Low High High
    Chronic Illness Low Low Low/Normal Low Normal/High
    Hemolytic Anemia High Normal/Low Low/Normal High High
    Sideroblastic Anemia Normal/High Normal/Low Low/Normal High High
    Iron Poisoning High Normal Low High Normal

    A high TIBC, UIBC, or transferrin usually indicates iron deficiency, but they are also increased in pregnancy and with the use of oral contraceptives.

    A low TIBC, UIBC, or transferrin may occur if someone has:

    Transferrin saturation is decreased with iron deficiency and increased when excess amounts of iron are present, as in iron overload or poisoning.

  • Is there anything else I should know?

    Recent blood transfusions can affect test results. Multiple blood transfusions can sometimes lead to iron overload.

  • Are there other things that cause anemia besides iron-deficiency?
    Yes, there are numerous causes of anemia. However, iron deficiency is the most common, which is why iron tests are so frequently performed. If iron tests rule out iron deficiency, another source for the anemia must be found. See the article on Anemia for more on this.
  • How is transferrin saturation calculated?
    The calculation is:

    Transferrin saturation (%) = (Serum iron level x 100%) / TIBC

  • What other factors affect the transferrin level?
    Transferrin is a protein that may decrease during any inflammatory process and is referred to as a negative acute phase reactant. Chronic inflammation, infections, and malignancies may cause changes in transferrin levels.
View Sources

Sources Used in Current Review

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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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(Updated 2007 August 24). Dietary Supplement Fact Sheet: Iron. NIH Office of Dietary Supplements [On-line information]. Available online at through Accessed June 2009.

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