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Iron · Blood
TIBC (total iron-binding capacity)
How much iron the transport protein transferrin can bind; needed to calculate transferrin saturation.
At a glance
- Measured in blood
- In 2 test panels
- No special preparation
Explanation
TIBC (total iron-binding capacity): what is measured?
Iron is carried in the blood by the protein transferrin, which can bind two iron atoms per molecule. The TIBC (in Dutch: TIJBC) is the total number of binding sites on transferrin and therefore another way of expressing the amount of transferrin, in µmol per liter. With iron deficiency, the body makes more transferrin and the TIBC rises; with iron overload, it falls. The TIBC is mainly used together with serum iron to calculate transferrin saturation.
What can it detect?
- Iron deficiency (raised TIBC, together with a low ferritin and a low saturation)
- Iron overload, including hereditary hemochromatosis (low TIBC, via a raised transferrin saturation)
- The distinction between iron deficiency and anemia in a chronic illness or inflammation (low TIBC)
Result
What does the result mean?
TIBC (total iron-binding capacity) too high
A raised TIBC means that there is a lot of transferrin in the blood. This fits iron deficiency: the body makes extra transferrin to be able to carry as much iron as possible. The TIBC also rises during pregnancy and with use of the contraceptive pill, without there being a deficiency. Whether there really is an iron deficiency is shown by the ferritin and the transferrin saturation. Symptoms that go with iron deficiency are tiredness, shortness of breath on exertion, hair loss and restless legs.
TIBC (total iron-binding capacity) too low
A low TIBC means that there is little transferrin in the blood. This occurs most often with inflammation or a long-lasting illness, because the body then makes less transferrin, and with liver disease, malnutrition or protein loss through the kidneys. The TIBC is also low with iron overload, such as hereditary hemochromatosis; the main sign of this is then a transferrin saturation above 45 percent, usually with a raised ferritin. Symptoms of iron overload only appear late: tiredness, joint pain, abdominal pain and darker skin.
After an abnormal result
The GP always assesses the TIBC together with serum iron, transferrin saturation, ferritin and, if needed, CRP. If the saturation is above 45 percent and ferritin is raised, the guideline recommends repeating the test and, if the rise persists, DNA testing for hemochromatosis (HFE genotyping). With a raised TIBC and a low ferritin, the cause of the iron deficiency is investigated.
Reliability
How reliable is the test?
According to the Dutch Society for Clinical Chemistry (NVKC), transferrin and TIBC give the same information in a different unit; laboratories usually report one of the two. On its own, the TIBC is not very specific, because inflammation, liver disease, pregnancy and the pill also change the value. Its meaning lies in the calculated transferrin saturation: according to the Dutch medical specialists' guideline (FMS) on hereditary hemochromatosis, a saturation above 45 percent is the threshold for further tests for iron overload. For iron deficiency, the Dutch GP guideline (NHG) on anemia uses ferritin as the first test.
What can affect the result?
- Inflammation, infections and long-lasting illness lower the TIBC, which can mask an iron deficiency.
- Pregnancy and the contraceptive pill raise the TIBC; liver disease, malnutrition and protein loss through the kidneys lower it.
- Some laboratories calculate the TIBC from the measured transferrin, others measure it directly; reference values therefore differ slightly.
- If in doubt, a raised transferrin saturation is repeated while fasting, because the serum iron in the calculation varies over the day and with meals.
Who it is for
Who is the test useful for?
Useful for
Useful as part of an iron profile (iron, TIBC or transferrin, transferrin saturation and ferritin) when iron overload is suspected, for example with hemochromatosis in the family or a previously raised ferritin, and when iron deficiency is suspected in someone with inflammation or a chronic illness. As a stand-alone value, the TIBC has little meaning; for an ordinary suspicion of iron deficiency, ferritin is the better test.
How common is it?
Anemia is newly diagnosed in general practice in about 9 in 1000 people per year; in half of them iron deficiency is the cause, in women about four times as often as in men. Hereditary hemochromatosis occurs in about 0.5 to 1.5 percent of the Northern European population, but only a small share of people with this predisposition develop symptoms.
NHG guideline on anemia and FMS guideline on hereditary hemochromatosis
Drawbacks and risks
- An abnormal TIBC due to pregnancy, the pill or inflammation can cause unnecessary worry without the other iron values.
- Confirmed hereditary hemochromatosis is also relevant for parents, brothers, sisters and children (an incidental finding with consequences for blood relatives).
Get tested
TIBC (total iron-binding capacity): test panels
TIBC (total iron-binding capacity) is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.
Evidence
Sources
This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.
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