Ferritin explained: what your iron blood test measures and what happens next

This guide is for adults in the UK who have had a ferritin blood test or need one soon. It explains what ferritin is and what the test measures. It also covers why clinicians read it alongside other results, and what usually happens next if your iron stores are low. However, it cannot tell you what your own result means. Only the clinician who asked for the test can do that.

What ferritin is

Your body uses iron to make haemoglobin, the part of your red blood cells that carries oxygen. Your body keeps any iron it does not need straight away in reserve, mostly bound to a protein called ferritin. In addition, a small amount of ferritin circulates in your blood, and that is what the test measures.^[6]

The amount in your blood tends to follow the amount in your stores. For this reason, clinicians use ferritin as a guide to your iron reserves, and some laboratories even list the test as “iron stores”.^[5] In fact, the British Society of Gastroenterology (BSG) describes ferritin as the single most useful blood marker of iron deficiency anaemia.^[1]

Why your doctor or nurse might check it

Clinicians usually ask for ferritin to look for iron deficiency, or to check how iron treatment is going. They also use it to look for the opposite problem, too much iron (iron overload). For example, this happens in a condition called haemochromatosis.^[4] However, this guide focuses on low iron.

Clinicians rarely look at ferritin on its own. Instead, they usually check it with a full blood count (FBC). This shows how much haemoglobin you have and whether you are anaemic.^[2] Low iron stores can also come before anaemia. In other words, your stores run down first, while your haemoglobin is still normal. The BSG calls this iron deficiency without anaemia.^[1] Our iron deficiency anaemia guide also explains the condition in more detail.

Having the test

The test uses an ordinary blood sample from your arm. The NHS says you do not need to do anything to prepare for a full blood count.^[2] Similarly, the NHS laboratory pages we checked list no fasting or other special preparation for a first ferritin test.^[4][6] However, if your GP or clinic gives you different advice, follow it.

Laboratories usually turn the test round within about a day.^[4] Even so, it can take longer for the result to reach you. The NHS says you may get blood test results after a few days, and usually within a few weeks. Some GP surgeries only get in touch if they need to talk to you about the result. So if you have not heard anything after a few weeks, contact the surgery.^[3] You may also be able to see your results in the NHS App.^[3]

Reading a ferritin result: why one number is not the whole story

Laboratories report ferritin in micrograms per litre (µg/L, sometimes written ug/L). Your number then appears next to a reference range. It is natural to want to compare the two, but there are three reasons to be careful.

Ranges differ between laboratories

Each laboratory sets its own reference range, depending on its equipment and population. Some also split the range by age and sex. For example, one NHS trust gives an adult range of 11 to 310 µg/L for women and 24 to 340 µg/L for men.^[5] Meanwhile, another trust uses different ranges for different age groups and hospital sites.^[4] So a number that looks “fine” on one report might mean something different elsewhere. For this reason, only compare your result with the range on your own report, and let your clinician interpret it.

“In range” is not always the same as “enough”

A reference range describes what is common in a population. However, that is not quite the same as what is healthy for you. The BSG guideline says a ferritin below 15 µg/L is “indicative of absent iron stores”. It adds that levels below 30 µg/L are “generally indicative of low body iron stores”.^[1] Some laboratories also add similar comments to their reports.^[6] Even so, your clinician reads your ferritin alongside your blood count, symptoms and medical history. That is why the same number can lead to different advice for different people.

Inflammation can push ferritin up

Doctors call ferritin an “acute phase protein” because its level rises when your body is dealing with infection or inflammation.^[4] As a result, ferritin can look normal even when iron stores are low, for example during an infection or a flare of an inflammatory condition.^[1][5] In that case, your clinician may also look at other blood tests. These include an inflammation marker (CRP) and transferrin saturation, which shows how much iron your blood is carrying.^[1]

On the other hand, a raised ferritin has its own list of possible reasons, and your GP or specialist will work through those. If your result is high, they may ask for a repeat test, sometimes on a fasting sample with transferrin saturation.^[4]

What usually happens next if your iron is low

Two things usually happen at the same time: treating the low iron, and finding out why it is low.

Treating the low iron

Most people start on iron tablets. The NHS says you will usually take them for up to 6 months, although some people need them long term. Meanwhile, your GP may repeat your blood tests over the next few months to check your iron is getting back to normal.^[2] The BSG recommends starting iron without waiting for other tests, unless a colonoscopy is about to happen. It also advises checking for a response in the first 4 weeks. After that, you carry on for around 3 months after your haemoglobin is back to normal, to refill your stores.^[1] If tablets do not suit you or do not work, other options include different tablets or iron through a drip.^[1] Our guide on how to take iron tablets also covers timing and side effects.

Finding the cause

Low iron is a sign that something has used up your stores. So the reason matters as much as the treatment. Things your GP or specialist will consider include blood loss, for example from heavy periods or from the gut. They also consider poor absorption of iron, pregnancy and diet.^[1][2] The tests your team suggests then depend on your age, sex, symptoms and blood results.

When someone has confirmed iron deficiency anaemia, the BSG recommends a urine test and a blood test for coeliac disease. In appropriate cases, it also recommends camera tests of the upper and lower gut.^[1] In men and in women after the menopause, that usually means a gastroscopy and a colonoscopy, often on the same day.^[1] Younger women are different, because periods are a common cause. In this group, the guideline suggests further tests after coeliac screening only if there are other features that need checking.^[1] In addition, your GP may arrange a poo test called FIT, which looks for tiny traces of blood.^[2][7] Our coeliac disease guide also explains the coeliac blood test.

A referral for a camera test can feel worrying. However, it does not mean your team thinks you have cancer. Most people who have these tests do not, and the tests often find something treatable, or nothing at all. If you have a gastroscopy, our guide to your gastroscopy report explains the common words you may see.

Getting ready for your appointment

Before you see your GP or the clinic, it helps to have your questions ready. For example, you could use this short list.

• Ask what your result means for you, and whether you need treatment, more tests or both.
• Ask when your repeat blood test should be, and who will check the result.
• Mention any medicines you take, such as over-the-counter painkillers and supplements.
• Note any tummy symptoms or changes in your poo before your appointment. For this, our free symptom diary can help.

When to get help

Frequently asked questions

Do I need to fast before a ferritin blood test?

Usually not. The NHS laboratory pages we checked list no special preparation for a first ferritin test.^[4][6] However, clinicians sometimes repeat a high ferritin on a fasting sample. In that case, follow the instructions from your GP or clinic.

Is ferritin the same as iron?

Not quite. Ferritin is the protein that stores iron, so it acts as a guide to how much iron you have in reserve. In contrast, tests such as transferrin saturation look at the iron your blood is carrying.^[1]

How long does it take for ferritin to go up on iron tablets?

Haemoglobin usually starts to rise within a couple of weeks, but refilling your stores takes longer. For example, the BSG suggests continuing iron for around 3 months after haemoglobin is back to normal. Similarly, the NHS says most people take tablets for about 6 months.^[1][2] Your GP or clinic will then tell you when to have your repeat test.

Why do I need a camera test for low iron?

The gut is one of the places where your body can lose iron or fail to absorb it. So, depending on your age, sex and other results, the BSG recommends checking the upper and lower gut with a gastroscopy and colonoscopy.^[1] Your team will also explain why they have suggested it for you.

Will I need more blood tests after my iron is back to normal?

Often, yes. The BSG suggests checking your blood count from time to time afterwards, perhaps every 6 months at first. That way, your team can spot low iron if it comes back.^[1] Your GP or clinic will then explain the plan for you.

References

1. Snook J, Bhala N, Beales ILP, et al. British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults. Gut. 2021;70(11):2030-2051. doi:10.1136/gutjnl-2021-325210. https://pmc.ncbi.nlm.nih.gov/articles/PMC8515119/
2. NHS. Iron deficiency anaemia. Page last reviewed 26 January 2024. https://www.nhs.uk/conditions/iron-deficiency-anaemia/
3. NHS. Blood tests. Page last reviewed 2 November 2023. https://www.nhs.uk/tests-and-treatments/blood-tests/
4. University Hospitals of North Midlands NHS Trust, Pathology. Ferritin. Reviewed 19 November 2025. https://www.uhnm.nhs.uk/our-services/pathology/tests/ferritin/
5. North Bristol NHS Trust, Severn Pathology. Ferritin. Accessed 12 November 2026. https://www.nbt.nhs.uk/severn-pathology/requesting/test-information/ferritin
6. York and Scarborough Teaching Hospitals NHS Foundation Trust, Laboratory Medicine. Ferritin. Accessed 12 November 2026. https://www.yorkhospitals.nhs.uk/our-services/a-z-of-services/lab-med/test-directory/clinical-biochemistry/ferritin
7. National Institute for Health and Care Excellence. Suspected cancer: recognition and referral (NG12), Recommendations. 2015, last amended 2025. https://www.nice.org.uk/guidance/ng12/chapter/Recommendations