Transferrin: what it is, what it tells you and when it’s tested

Transferrin is the protein that carries iron in your blood. Your liver makes it. It picks up iron absorbed by the gut or released from your stores and takes it where it is needed, above all to the bone marrow, where red blood cells are made. When iron runs short, your body makes more of it.

When it’s tested

Doctors order it with serum iron, to work out transferrin saturation. It helps when they suspect iron is short or too high, especially if inflammation makes ferritin unreliable.

Sometimes they also ask for it to see how your liver and nutrition are doing, together with albumin.

Rosa does not test it on its own, because it already measures what is needed to read your iron: ferritin, serum iron, TIBC and transferrin saturation. Many labs derive the TIBC from transferrin itself.

What it tells you, and what it does not

If it is high, iron is usually running short: your body makes more seats to catch more of it.

If it is low, inflammation is the most common reason. Less often a liver condition, poor nutrition, protein loss or too much iron.

On its own it does not say how much iron you have in store: ferritin does that. It is always read with the other iron tests.

That is why it is read together with other tests:

• Ferritin: How much iron you have in store
• Transferrin saturation: How many of the seats are taken by iron
• Serum iron: The iron in circulation today
• TIBC: All the seats for iron, derived from transferrin

Normal transferrin levels

The lab decides what is normal. Many lab reports give 200 to 360 mg/dL in adults. Some write g/L, with the decimal point moved, and some print a slightly lower upper limit.

It is on average a little higher in women than in men. It rises in pregnancy and on the pill.

If you are just outside the limits and your ferritin and saturation are normal, it is usually not a worry.

What your result means

Find the row for your result, in mg/dL. On its own it is rarely enough: look at ferritin and saturation too.

• Below 200: Low. Most often inflammation. Less often the liver, poor nutrition, protein loss or too much iron. Show it to your doctor, with ferritin, saturation and CRP.
• 200 to 360: Normal. Your blood has enough seats to carry iron. Nothing to do. What counts is how it reads with the other iron tests.
• Above 360: High. Usually iron is running short. It also rises in pregnancy and on the pill. Look at your ferritin and talk to your doctor.

If your transferrin is high or low

• Low transferrin: Most often inflammation. Sometimes the liver, nutrition, protein loss or too much iron.
• High transferrin: Usually iron is running short. It also rises in pregnancy and on the pill. The causes are below.

What causes high transferrin

Usually iron, sometimes hormones.

• Iron is short: The most common cause. It usually comes with low ferritin and saturation.
• Pregnancy: It rises naturally, especially towards the end. In pregnancy, iron tests are read with your gynaecologist.
• The pill and hormone therapy: Oestrogens raise it. Do not stop them on your own: tell your doctor when you go through your report.

What can skew the result

Transferrin changes little through the day, but a few things shift it.

• A recent inflammation: An infection or other inflammation lowers it for a while. If you were ill recently, your doctor may repeat it.
• The pill and pregnancy: Both raise it. Tell your doctor when they read your report.
• The lab’s method: The limits vary a little from lab to lab. To compare two results, it is best to use the same lab.
• Fasting: Not needed for transferrin itself. But it is done with serum iron, which asks for it, so it is best to come fasting, in the morning.

When to worry

Transferrin on its own is rarely a reason to see a doctor. Talk to your doctor if:

• It is high and your ferritin is low: iron is usually short, and the reason needs to be found.
• It is low and your CRP is high, or you have lost weight without trying.
• It is low and your transferrin saturation is high.
• You have swollen legs, very foamy urine or yellow skin.
• You have black stools or a lot of blood in your stools: call 112 or go to the emergency department.

Frequently asked questions

What are normal transferrin levels? Many lab reports give 200 to 360 mg/dL in adults, but the limits vary a little between labs. The range printed next to your result is what counts.

What is the difference between transferrin and ferritin? Transferrin carries iron in your blood. Ferritin shows how much iron you have in store. When iron runs short, ferritin falls and transferrin rises.

What is the difference between transferrin and TIBC? Transferrin is the protein, in mg/dL. TIBC shows how much iron it can carry in total, in µg/dL. Many labs derive TIBC from transferrin with a fixed factor, which is why they move together. The numbers cannot be compared directly, though.

High transferrin: what does it mean? Usually that iron is running short, especially if ferritin is low. It also rises in pregnancy and on the pill, without any iron shortage.

Does Rosa test transferrin? Not as a separate test. Rosa measures ferritin, serum iron, TIBC and transferrin saturation, which together show how much iron you have and how much reaches where it is needed. If your doctor wants transferrin, they order it separately.

Sources

• Liverpool University Hospitals, serum transferrin laboratory test sheet: adult reference interval. Liverpool University Hospitals NHS, serum transferrin
• Eurofins Biomnis, Précis de biopathologie: transferrin, causes of change and relation to total iron-binding capacity. 2013. Eurofins Biomnis, Précis de biopathologie, Transferrine
• Gambino and colleagues, the relation between chemically measured total iron-binding capacity and immunologically measured transferrin in human serum. Clinical Chemistry, 1997. PMID 9439462
• Ritchie and colleagues, reference distributions for the negative acute-phase serum proteins, albumin, transferrin and transthyretin. Journal of Clinical Laboratory Analysis, 1999. PMID 10633294
• Snook and colleagues, British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults. Gut, 2021. PMID 34497146