Iron
Transferrine
The protein that carries iron through the blood; needed to calculate the transferrin saturation in iron deficiency or iron overload.
Everything about this testWhat it measures
Transferrin is the protein that carries iron through the blood, from the gut and the body's stores to the bone marrow; each molecule can bind two iron atoms. The test measures how much transferrin is in the blood, in grams per liter. In iron deficiency the liver makes more transferrin, in iron overload and inflammation less. In the Netherlands, transferrin is mainly measured to calculate, together with serum iron, the transferrin saturation: the percentage of transferrin that is loaded with iron.
- Iron deficiency (raised transferrin, together with a low ferritin and a low saturation)
- Iron overload, including hereditary hemochromatosis (low transferrin, via a saturation above 45 percent)
- Distinguishing between iron deficiency and anemia due to a chronic disease or inflammation (low transferrin)
High
A raised transferrin fits iron deficiency: the body makes extra transport protein to absorb and carry as much iron as possible. Transferrin is also higher during pregnancy and when using 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 during exertion, hair loss and restless legs; in endurance athletes, a deficiency can also reduce stamina.
Low
A low transferrin is most often seen with inflammation, infection or long-term illness, because less transferrin is made then. Other causes are liver disease, malnutrition and protein loss through the kidneys. Transferrin is also low in iron overload, such as hereditary hemochromatosis; the sign of this is then a transferrin saturation above 45 percent, usually together with a raised ferritin. Rarely: a hereditary lack of transferrin. Symptoms of iron overload only appear late: tiredness, joint pain, abdominal pain and a darker skin.
If your result is abnormal
The GP always assesses transferrin together with the serum iron, the transferrin saturation, the ferritin and, if needed, CRP. If the saturation is above 45 percent and the ferritin is raised, the guideline recommends a repeat and, if the rise persists, DNA testing for hemochromatosis (HFE genotyping). With a raised transferrin and a low ferritin, the cause of the iron deficiency is investigated.
Reliability
The measurement of transferrin is accurate and, according to the Dutch medical specialists' guideline (FMS) on hereditary hemochromatosis, the reference values hardly differ between Dutch laboratories. On its own, transferrin 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 that guideline, a saturation above 45 percent is the threshold for further testing for hereditary hemochromatosis. For iron deficiency, the Dutch GP guideline (NHG) on anemia uses ferritin as the first test.
Limitations
- Transferrin is a negative acute phase protein: inflammation, infections and long-term illness lower the value and can mask an iron deficiency.
- Pregnancy and the contraceptive pill raise transferrin; liver disease, malnutrition and protein loss through the kidneys lower it.
- If in doubt, a raised transferrin saturation is repeated while fasting, without iron or vitamin supplements in the 24 hours before, because the serum iron used in the calculation fluctuates strongly.
- Reference values can differ slightly between laboratories.
How common is this
In general practice, anemia newly occurs in about 9 in 1000 people per year; in half of them iron deficiency is the cause, about four times as often in women 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.
Who is this useful for
Useful as part of an iron profile (iron, 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 with inflammation, a chronic disease or a lot of endurance sport. As a stand-alone value, transferrin has little meaning; for an ordinary suspicion of iron deficiency, ferritin is the better test.
Downsides and risks
- An abnormal transferrin due to pregnancy, the pill or inflammation can cause unnecessary worry without the other iron values.
- A confirmed hereditary hemochromatosis also matters for parents, brothers, sisters and children (an incidental finding with consequences for blood relatives).
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results