About the Test
Purpose of the test
The transferrin, TIBC, or unsaturated iron-binding capacity (UIBC) test may be used along with other iron tests to assess the amount of iron circulating in the blood, the total capacity of the blood to transport iron, and the amount of stored iron in the body. Testing may also help differentiate various causes of anemia.
Iron tests are often ordered together, and the results of each can help identify iron deficiency, iron deficiency anemia, or too much iron in the body (overload).
What does the test measure?
Iron is an essential nutrient that, among other functions, is necessary for producing 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 body parts. 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, produced by the liver. If you are healthy, most iron is incorporated into the hemoglobin within developing RBCs in bone marrow. The remainder is stored in the tissues as ferritin or hemosiderin, with additional small amounts used for other purposes (e.g., to produce other iron-containing proteins such as myoglobin and some enzymes).
The transferrin test, TIBC, UIBC, and transferrin saturation, along with other iron tests, help evaluate the body’s amount by measuring several substances in the blood. These tests are often ordered simultaneously, and the results are interpreted together to help diagnose and/or monitor iron deficiency or 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 protein level in the blood. The level depends upon liver function and your nutritional status. Transferrin, a protein that may decrease during any inflammatory process, is referred to as a negative acute phase reactant.
- TIBC — measures the total amount of iron that can be bound by transferrin proteins in the blood. Since transferrin is the primary iron-binding protein, the test is a good indirect measurement of transferrin availability, the amount of transferrin available to bind to iron. (Note: Though TIBC is a reflection of the amount of transferrin available, TIBC and transferrin are not synonymous.)
- UIBC — this test determines the reserve capacity of transferrin, i.e., the portion not yet saturated with iron.
- Transferrin saturation — dividing the iron concentration by the TIBC produces an estimate of the percentage of occupied transferrin iron-binding sites, called the transferrin saturation (%). Under normal conditions, transferrin is one-third saturated with iron, so 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 or the transferrin index.)
- Ferritin — measures the level of this protein made by almost all cells in response to increased iron. The ferritin level reflects the total storage of iron in the body. 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 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, excess menstrual bleeding)
- 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. The amount of iron stored may be significantly depleted before any signs or symptoms of iron deficiency develop.
If you are otherwise healthy and anemia develops over a long period, symptoms may not appear before the hemoglobin in the blood drops significantly below the lower limit of normal due to gradual body adaptation.
However, as iron deficiency progresses, symptoms eventually begin to appear. The most common symptoms of anemia include fatigue, weakness, dizziness, headaches, and pale skin.
Conversely, too much iron can be toxic. 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 you undergo repeated blood transfusions for various transfusion-dependent anemias.
When should I get this test?
These tests may be ordered along with other iron tests when results from a routine CBC show that your hemoglobin and hematocrit are low and your red blood cells are smaller and paler than normal (microcytic and hypochromic), suggesting iron deficiency anemia even though other clinical symptoms may not have developed yet.
Iron tests may be ordered when you develop signs and symptoms of anemia such as:
- Chronic fatigue/tiredness
- Pale skin (pallor)
Testing may be ordered when iron overload is suspected. Signs and 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. These may include:
- Joint pain
- Fatigue, weakness
- Weight loss
- Lack of energy
- Abdominal pain
- Loss of sex drive
- Organ damage, such as in the heart and/or liver
Testing is also ordered when there is a case of suspected iron poisoning. This is most common in children who accidentally overdose on vitamins or other supplements containing iron.
Finding a Transferrin and Iron-binding Capacity Test
How can I get a transferrin and iron-binding capacity test?
Your doctor usually orders transferrin and iron-binding capacity if previous testing has shown that you have low hemoglobin and hematocrit or your red blood cells are smaller than normal.
You can also order a TIBC test online without a doctor’s order.
Can I take the test at home?
While you can purchase a TIBC test at home, you will need to visit a laboratory to have your blood sample taken.
How much does the test cost?
The cost of a TIBC test will vary based on several factors, such as where your blood test sample is taken and your health insurance coverage. If a doctor prescribes the test, your insurance company may pay for some or all of these costs. For the most definitive information about what a test will cost you, talk with your doctor’s office and medical insurance company.
Taking a Transferrin and Iron-binding Capacity Test
TIBC testing requires a blood sample from a vein in your arm.
Before the test
You may need to fast for eight to 12 hours before your blood test. Follow any instructions provided with your online test or by your doctor.
During the test
A need will be inserted into a vein in your arm and a vial of blood withdrawn. The process involves minimal pain, although some patients report a burning or stinging at the needle injection site. The total blood draw usually lasts only a few minutes.
After the test
Once you have done the test, the technician will place a cotton swab and/or bandage over the puncture site to stop any bleeding. You can generally return to normal activities once the test is over, although the lab technician will let you know if there are any restrictions, such as avoiding heavy lifting. You may feel slight pain or bruising at the injection site, but this normally goes away quickly.
Transferrin and Iron-binding Capacity Test Results
Receiving test results
TIBC test results are typically available within a few business days of the lab receiving your sample. You may receive your results via mail or through an online health portal.
Your doctor may contact you to discuss your results and schedule a follow-up appointment.
Interpreting test results
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.
(e.g., infection, cancer)
The early stage of iron deficiency is the slow depletion of iron stores. This means there is still enough iron to make red cells but the stores are being used up without adequate replacement. The serum iron level may be normal in this stage, but the ferritin level will be low.
As iron deficiency continues, all of the stored iron is used and the body tries to compensate by producing more transferrin to increase iron transport. The serum iron level continues to decrease and transferrin and TIBC and UIBC increase. As this stage progresses, fewer and smaller red blood cells are produced, eventually resulting in iron deficiency anemia. Transferrin saturation is decreased with iron deficiency.
If the iron level and transferrin saturation are high, the TIBC, UIBC and ferritin are normal and you have a clinical history consistent with iron overdose, it is likely you have iron poisoning.
This occurs when a large dose of iron is taken all at once (acute) or over a long period of time (chronic). Iron poisoning in children is almost always acute, occurring in children who ingest their parents’ iron supplements. In some cases, acute iron poisoning can be fatal.
If you have mutations in the homeostatic iron regulator (HFE) gene or another iron regulation gene you are diagnosed with hereditary hemochromatosis. But while many people who have hemochromatosis will have no symptoms for their entire life, others start to develop symptoms such as joint pain, abdominal pain, and weakness in their 30s or 40s.
Men are affected more often than women because women lose blood during their reproductive years through menstruation.
Iron overload may also occur if you have hemosiderosis and have had repeated transfusions. This may occur with sickle cell anemia, thalassemia major, or other forms of anemia. The iron from each transfused unit of blood stays in the body, eventually causing a large buildup in the tissues. Some persons with alcoholism and chronic liver disease also develop iron overload.
When you talk with your doctor, some of these questions may be helpful to review:
- Were my results high, low or normal?
- If my results were too high or too low, what do you think is the most likely cause?
- Were any other measurements taken along with TIBC or UIBC? If so, were they normal or abnormal?
- Are there any follow-up tests that you recommend?