Key takeaways
- Ferritin reflects how much iron your body has stored, which makes it the single most useful test for suspected iron deficiency.
- Infection, inflammation and liver problems can push ferritin up, so a doctor reads it with the other iron markers.
- Iron, total iron-binding capacity (TIBC) and transferrin saturation show how iron is being carried, and fill in the rest of the picture.
- Testing before you start supplements tells you whether low iron is really the cause, and what to look at next.
You have been tired for weeks, more of your hair is ending up in the brush, or the stairs leave you short of breath. A friend says it sounds like low iron.
Ferritin shows how much iron is stored in your body. Iron, TIBC and transferrin saturation show how much iron is 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.
If you would rather find out than keep guessing, book a ferritin blood test at 117a Harley Street. It costs £68.75 plus the £50 blood draw, with results in 1 day.
What does ferritin actually measure?
Ferritin is a protein that stores iron. The amount in your blood reflects how much iron your body has in reserve, as opposed to 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 with heavy periods, restricted or plant-based diets, pregnancy, or a digestive condition that affects how iron is absorbed. It is a frequent cause of tiredness and hair loss.
Why can ferritin look normal when I am actually iron deficient?
Ferritin also rises with infection, inflammation and liver problems. So it can look normal, or even high, in someone who is genuinely iron deficient. Doctors call it an acute phase protein: levels go up as part of the body's general response to illness, whatever your iron stores are doing.
That is why a clinician reads ferritin alongside a full blood count and the other iron markers. Our guide to full blood count results explains that test. It is also why a normal ferritin during or just after an infection can be less reassuring than it looks.
What do iron, TIBC and transferrin saturation add to the picture?
Iron and total iron-binding capacity show how much iron is in your blood now, and how much spare capacity your blood has to carry more. Blood London offers them together as one iron and TIBC test for £43.75, with results in 1 day.
Transferrin saturation is calculated from iron and TIBC. It shows what proportion of your iron-carrying protein is actually loaded with iron. Low ferritin with low iron and low transferrin saturation commonly points to true iron deficiency. High ferritin with normal or low transferrin saturation is more likely to reflect inflammation than iron overload.
The table below shows 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 usually comes down to taking in too little, 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 absorption even when intake is fine.
Working out which applies is why a doctor's review matters once deficiency is confirmed. In men, and in women after the menopause, unexplained iron deficiency should always be investigated by a doctor. 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, there is a wider option. The tiredness and brain fog blood test checks iron status alongside thyroid, B12 and other markers that can explain fatigue. It costs £395, with results in up to 2 working days, and a fasting morning sample is preferred.
Is it worth testing before I start iron supplements?
Yes. Too much iron over time can be harmful. A test also tells you whether low iron is really behind your tiredness or whether something else needs looking at. Recent supplements can also affect iron and ferritin levels, which can make a test taken soon afterwards harder to read.
If you already take iron, folate or B12 supplements, tell the phlebotomist what you take and when you last took it.
What happens if my results show a deficiency or overload?
A doctor can advise on the likely cause and the right next step. That may mean dietary changes, supplements, or further tests to understand why the deficiency or overload developed. Because several of these markers move together, a doctor looks at the whole pattern alongside your symptoms and diet. This matters most when ferritin, iron and transferrin saturation point in different directions.
Sometimes a full blood count is needed to confirm anaemia. The Anaemia Profile combines iron, ferritin, folate and B12 with a full blood count and ESR in one visit. It costs £226.25, with results in 2 days.
How testing works at Blood London
You can walk in or book online at 117a Harley Street, seven days a week, with no GP referral needed. No fasting is needed, so you can come at any time. Iron levels vary through the day, though, so if your doctor has asked for a morning sample or given other instructions, follow those. Results are usually back within 1 day and sent to you by email.
For the fuller picture, the Iron Status Profile combines iron with TIBC, ferritin and transferrin saturation for £126.25. Results also take 1 day. Each test price on this page is plus the £50 blood draw, as with all our private blood tests in London. When you are ready, 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 circulating in your blood at that moment, which is why the two are usually read together.
Do I need to fast before a ferritin or iron test?
Fasting is not usually required for either test. Iron levels vary through the day, so follow any 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 early on. That is one reason iron markers are often included in wider health checks.
Should I stop my iron or B12 supplements before the test?
You may not need to stop. Tell the phlebotomist what you take and when you last took it, since recent supplements can affect the results and how they are read.
How is iron deficiency confirmed if ferritin alone is unclear?
Iron, TIBC and transferrin saturation are used alongside ferritin, sometimes with a full blood count, when inflammation makes ferritin hard to read. The combined pattern, read by a doctor, is more reliable than any single result.
Where can I get help if my results are abnormal?
Talk them through 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 lasted, consider a doctor-led fatigue assessment at Medical Express Clinic. It 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