Key takeaways
- Ferritin reflects how much iron your body has stored, which makes it the single most useful test for suspected iron deficiency.
- At Blood London, a ferritin test costs £68.75 plus the £50 blood draw, with results back in 1 day.
- Ferritin can be pushed up by infection, inflammation or liver problems, so a normal ferritin does not always rule out iron deficiency.
- Iron and total iron-binding capacity (TIBC), and transferrin saturation, are read alongside ferritin for a fuller picture.
- Low iron should be confirmed and its cause investigated before starting supplements, rather than self-treating on suspicion alone.
- No fasting is needed for either test.
Ferritin shows how much iron is stored in your body, while iron, TIBC and transferrin saturation show how much iron is currently circulating and how well it is being carried. Together they help explain tiredness, breathlessness or hair loss that could be linked to low iron. You can book a ferritin blood test at Blood London without a GP referral.
Book a ferritin blood test at 117a Harley Street: £68.75 plus the £50 blood draw, results in 1 day.
What does ferritin actually measure?
Ferritin is a protein that stores iron, so the amount in your blood reflects how much iron your body has in reserve rather than how much is circulating at that moment. It is usually the first test a doctor looks at when iron deficiency is suspected, because it tends to fall before other markers change. Low ferritin is common in people with heavy periods, restricted or plant-based diets, pregnancy, or a digestive condition that affects how iron is absorbed, and it is a frequent cause of tiredness and hair loss.
Why can ferritin look normal when I am actually iron deficient?
Ferritin can look normal, or even high, in someone who is genuinely iron deficient, because it also rises with infection, inflammation and liver problems. Ferritin behaves as what is known as an acute phase protein, meaning levels go up as part of the body's general response to illness, independently of iron stores. This is why a clinician reads ferritin alongside a full blood count (see our guide to full blood count results) and the other iron markers, rather than on its own, and why a normal ferritin during or shortly after an infection is not always reassuring.
What do iron, TIBC and transferrin saturation add to the picture?
Iron and total iron-binding capacity show how much iron is currently in your blood and how much spare capacity your blood has to carry more of it, which together with ferritin gives a fuller picture than ferritin alone. Blood London offers them together as one iron and TIBC test for £43.75 plus the £50 blood draw, with results in 1 day. Transferrin saturation, calculated from iron and TIBC, shows what proportion of your iron-carrying protein is actually loaded with iron. Low ferritin alongside low iron and low transferrin saturation commonly points towards true iron deficiency, while a pattern of high ferritin with normal or low transferrin saturation is more likely to reflect inflammation rather than iron overload.
The table below summarises how the main patterns are usually read.
| Pattern | Ferritin | Iron / transferrin saturation | Usual interpretation |
|---|---|---|---|
| Iron deficiency | Low | Low | Depleted iron stores, the most common pattern in deficiency |
| Inflammation or infection | Normal or high | Often low or normal | Ferritin raised by the acute phase response, not by iron stores |
| Iron overload | High | High | Needs further assessment, as high ferritin has several causes |
| Combined deficiency and inflammation | Normal | Low | The pattern most likely to mask a true deficiency |
What can cause low iron in the first place?
Low iron most often comes down to not taking in enough iron, losing more than usual, or absorbing less than usual. Heavy periods, pregnancy and gradual blood loss elsewhere in the body are common causes of loss. Restricted, vegetarian or vegan diets can mean lower intake if not carefully planned. Digestive conditions that affect the gut lining can reduce how much iron is absorbed even when intake is adequate. Working out which of these applies is why a doctor's review matters once deficiency is confirmed, rather than assuming the cause. In men, and in women after the menopause, iron deficiency without an obvious cause should always be investigated by a doctor, because it can come from hidden bleeding in the gut. Black or bloody stools, or unexplained weight loss, mean seeing a doctor promptly. Where tiredness is the main complaint and the cause is unclear, a wider tiredness and brain fog blood test looks at iron status alongside thyroid, B12 and other markers that can also explain fatigue (£395 plus the £50 blood draw, results in up to 2 working days; a fasting morning sample is preferred).
Why shouldn't I just start iron supplements without testing?
Starting iron supplements without testing first is not advised, because too much iron over time can be harmful, and supplementing when you are not actually deficient will not fix tiredness that has another cause. Iron and ferritin levels can also be affected by recent supplementation, which can make it harder to interpret a test taken soon afterwards. If you are already taking iron, folate or B12 supplements, tell the phlebotomist what you are taking and when you last took it before your sample is taken.
What happens if my results show a deficiency or overload?
A doctor can advise on the likely cause and the appropriate next step, which may include dietary changes, supplements, or further tests to understand why the deficiency or overload developed. Because several of these markers move together, a doctor typically looks at the whole pattern alongside your symptoms and diet rather than any single result, particularly when ferritin, iron and transferrin saturation do not all point the same way. Where a full blood count is also needed to confirm anaemia, the Anaemia Profile combines iron, ferritin, folate and B12 with a full blood count and ESR in one visit (£226.25 plus the £50 blood draw, results in 2 days).
How testing works at Blood London
A ferritin test costs £68.75 plus the £50 blood draw, and results are usually back within 1 day. The Iron Status Profile, which combines iron with TIBC, ferritin and transferrin saturation, costs £126.25 plus the £50 blood draw, also with results in 1 day. Iron levels can vary through the day, so if your doctor has asked for a morning sample or given other specific instructions, follow those; otherwise no fasting is needed and you can attend at any time. As with all our private blood tests in London, you can walk in or book online at 117a Harley Street, seven days a week, with no GP referral needed, and results are sent to you by email.
Book a ferritin blood test at 117a Harley Street: £68.75 plus the £50 blood draw, results in 1 day. Start your booking.
Frequently asked questions
What is the difference between ferritin and an iron test?
Ferritin shows how much iron is stored in your body. An iron test measures the iron currently circulating in your blood at that moment, which is why the two are usually read together rather than in isolation.
Do I need to fast before a ferritin or iron test?
No, fasting is not usually required for either test. Iron levels can vary through the day, so follow any specific timing instructions your doctor has given you.
Can I be low in iron without feeling tired?
Yes, some people have low iron stores with few or no symptoms, particularly in the early stages. That is one reason iron markers are often included in wider health checks rather than only when symptoms appear.
Should I stop my iron or B12 supplements before the test?
You do not necessarily need to stop, but tell the phlebotomist what you are taking and when you last took it, since recent supplementation can affect the results and how they are interpreted.
How is iron deficiency confirmed if ferritin alone is unclear?
Iron, TIBC and transferrin saturation are used alongside ferritin, and sometimes a full blood count, to build a fuller picture when ferritin is difficult to interpret because of inflammation. The combined pattern, read by a doctor, is more reliable than any single result.
Where can I get help if my results are abnormal?
Discuss abnormal results with your GP or a private doctor, or add a doctor review to your test at Blood London for £75. If tiredness is the main problem and has not settled, a doctor-led fatigue assessment at Medical Express Clinic reviews your results alongside an examination and wider tests.
References
- NHS: Iron deficiency anaemia
- Lab Tests Online UK: Ferritin test
- Lab Tests Online UK: Iron and TIBC
- NICE CKS: Anaemia, iron deficiency
- British Society for Haematology: Guidelines on iron deficiency