Iron deficiency anaemia is one of the most common blood problems in the UK, and one of the most common reasons people are referred to a gastroenterology clinic. This guide explains what it is, why your GP might send you for a camera test, how to take iron so it actually works, when an iron infusion makes sense, and what to expect afterwards.
Key points
- Anaemia means your haemoglobin (the oxygen-carrying part of your blood) is low. Iron deficiency is the most common cause.
- Tiredness, breathlessness, headaches and looking pale are typical, but some people have no symptoms at all.
- In men and in women after the menopause, iron deficiency anaemia is usually investigated with camera tests of the stomach and bowel, because slow bleeding from the gut is a common cause.
- One iron tablet a day, taken on an empty stomach, works as well as larger doses for most people, with fewer side effects.
- Keep taking iron for about 3 months after your blood count is back to normal, to refill your stores.
What is iron deficiency anaemia?
Your body uses iron to make haemoglobin, the protein in red blood cells that carries oxygen around your body. When your iron stores run low, you can’t make enough haemoglobin, and you become anaemic.
Anaemia is diagnosed from a full blood count. In adults it’s usually defined as a haemoglobin level below 130 g/L in men and below 120 g/L in women who aren’t pregnant, although labs use slightly different ranges.[1,2] Iron stores are measured with a blood test called ferritin. A low ferritin confirms that the anaemia is caused by a lack of iron. Ferritin can be falsely normal or high when there’s inflammation in the body, so your doctor may look at other iron tests too.[1]
Iron deficiency without anaemia
You can have low iron stores with a normal haemoglobin. This is called iron deficiency without anaemia. It can still cause tiredness and is usually treated with iron, but it doesn’t automatically mean you need camera tests.[1]
Symptoms
- tiredness and lack of energy
- feeling short of breath, especially on stairs or when exercising
- a fast or pounding heartbeat (palpitations)
- headaches, and finding it hard to concentrate
- pale skin
- less common: hair thinning, a sore tongue, cracks at the corners of the mouth, restless legs, or craving ice
Many people put these symptoms down to being busy or getting older. Because iron deficiency usually develops slowly, the body adapts, and some people only realise how tired they were once they’re treated.
See your GP promptly, and don’t wait for your next routine appointment, if you have iron deficiency anaemia and:
- you’ve seen blood in your poo, or your poo is black or tarry (and you aren’t taking iron)
- you’re losing weight without trying
- you have a change in your bowel habit that has lasted a few weeks
- you have difficulty swallowing, or persistent indigestion or tummy pain
- you feel very breathless, dizzy or faint, or have chest pain
If you are vomiting blood, passing a lot of blood, or have chest pain, call 999 or go to A&E.
What causes it?
Iron deficiency happens when you lose more iron than you take in, or can’t absorb enough. The common causes are:[1]
- Blood loss from the gut. Slow, hidden bleeding from the stomach or bowel, for example from inflammation, ulcers, polyps or, less often, cancer. Anti-inflammatory painkillers such as ibuprofen and aspirin are a common cause of this. See our guide to gastritis.
- Heavy periods. This is the most common cause in women who still have periods.
- Not absorbing iron properly. Coeliac disease is found in around 3 to 5 in every 100 people with iron deficiency anaemia.[1] Previous stomach surgery, long-term acid-reducing medicines and the stomach infection H. pylori can also reduce absorption.
- Not enough iron in the diet. This is less common in the UK, but more likely with a restricted diet.
- Pregnancy, when the body needs much more iron.
- Blood donation, if you give blood often.
Tests you may be offered
UK guidance recommends looking for the cause, not just treating the anaemia.[1] What you’re offered depends on your age, sex and symptoms.
Tests for everyone
- a blood test for coeliac disease[1,4]
- a urine test to check for blood in your urine
- a FIT test, a home poo test that detects tiny amounts of blood. NICE recommends it for adults with iron deficiency anaemia to help decide how quickly they need to be seen.[3]
Camera tests
For men of any age and women who no longer have periods, the usual next step is a gastroscopy to look at the stomach and a colonoscopy to look at the large bowel.[1] They’re often done on the same day. If a colonoscopy isn’t suitable, a CT scan of the bowel (CT colonography) may be used instead. Some units offer a transnasal endoscopy instead of a standard gastroscopy.
For women who still have periods, camera tests aren’t usually needed unless there are other symptoms, a strong family history of bowel cancer, or the anaemia seems out of proportion to the periods.[1]
If the camera tests are normal and the anaemia keeps coming back, a capsule endoscopy may be used to look at the small bowel.[1]
How urgent is it?
NICE uses age, symptoms and the FIT result to decide whether you need a suspected cancer pathway referral, which means being seen within a couple of weeks.[2,3] Being referred this way doesn’t mean cancer is likely. It means your tests are prioritised. Most people investigated for iron deficiency anaemia don’t have cancer, and many have a simpler, treatable cause.
Why I always look for the cause
I run an iron deficiency anaemia clinic and help vet the urgent referrals that come in for it, so I see this from both ends: the letter from the GP, and the person in front of me worried about what it means.
If you take one thing from this guide, let it be this: iron treats the anaemia, but it doesn’t explain it. In men and in women after the menopause, the gut is the commonest place for hidden blood loss, and some of the causes, such as polyps or coeliac disease, need treatment of their own.
Not everyone needs the same tests. When we decide whether you need them, which ones and how soon, we look at the whole picture: how long you’ve had anaemia, the type of anaemia, your symptoms and history, any tests you’ve had before, and screening results such as a FIT test.
It’s also worth knowing that, even after careful tests, we don’t always find one clear cause, and that’s quite common. Often it’s about putting the pieces of the jigsaw together, such as your diet, periods, medicines and test results, to work out the most likely explanation, while making sure we’ve ruled out anything serious.
The other half of my job is practical. Getting the iron to work is often about small changes, like taking your tablet first thing with water and moving your cup of tea an hour later. An iron infusion is a good option if you’ve tried at least two different iron tablets that haven’t worked or that you couldn’t tolerate, or if your anaemia is severe or causing significant symptoms. Nobody should feel they’ve failed for needing one.
Ben JohnsonAdvanced Clinical Practitioner, Gastroenterology
Treatment: how to take iron properly
Iron tablets are cheap, safe and effective, but how you take them makes a big difference.
- One tablet a day. UK guidance recommends one tablet of ferrous sulphate, ferrous fumarate or ferrous gluconate daily.[1,5] Larger doses aren’t absorbed any better, and cause more side effects.
- Every other day is an option if daily tablets upset your stomach. A dose triggers a hormone (hepcidin) that blocks absorption for about a day, so alternate-day doses may be absorbed just as well.[1,6] Ask your GP or pharmacist first.
- On an empty stomach, ideally an hour before food. Tea, coffee, milk and antacids reduce absorption, so keep them at least an hour or two away from your tablet.
- Keep going. Your haemoglobin should start to rise within 2 to 4 weeks. Once it’s back to normal, carry on for about 3 months to rebuild your iron stores.[1,5]
Side effects
Side effects are common: indigestion, nausea, constipation or loose stools, and black poo. Black poo from iron is normal and harmless. If you’re unsure whether it’s from the iron or from bleeding, speak to your GP. If side effects are a problem, try taking the tablet with a small amount of food, switching to alternate days, or ask about a different type of iron. A liquid iron can be easier for some people.
Before a colonoscopy or capsule test: you’ll usually be asked to stop iron tablets about a week before, because iron makes the bowel harder to see. Your letter will tell you.
Iron infusions
Iron can be given straight into a vein (an iron infusion) if tablets don’t work, can’t be tolerated, or the anaemia needs correcting quickly, for example before surgery, in inflammatory bowel disease, or with ongoing bleeding.[1] One or two infusions, each taking from a few minutes to half an hour or so depending on the product, can replace your iron stores in one go. Serious reactions are rare, and you’ll be watched for a short time afterwards.
Blood transfusion
A transfusion is only needed for very severe anaemia, or if you’re actively bleeding or very unwell. Most people with iron deficiency anaemia never need one.
Follow-up
Once your blood count is normal, it’s usually checked every few months for the first year, then less often, often with a ferritin test.[1] If iron deficiency comes back, more iron usually works, and your doctor will decide whether further tests are needed. Keeping a note of how you feel, alongside your results, helps: our free 7-day symptom diary has space for this.
Eating for iron
Diet alone rarely fixes iron deficiency anaemia, but it helps keep your stores up afterwards.[7] Good sources include red meat, fish, beans and lentils, tofu, dark green vegetables, dried fruit and iron-fortified breakfast cereals. Iron from plant foods is absorbed better alongside foods rich in vitamin C, such as fruit, peppers or tomatoes, and less well alongside tea or coffee.
Frequently asked questions
How long does it take to feel better?
Many people notice more energy within a few weeks of starting iron. Your haemoglobin usually rises noticeably within 2 to 4 weeks, but filling your iron stores takes several months.
Should I take vitamin C with my iron tablet?
It isn’t routinely needed. Taking your tablet on an empty stomach, away from tea and coffee, matters more. Your doctor may suggest it if your iron isn’t rising as expected.
Why do I need a camera test if I just need iron?
Because the cause matters. In men and in women after the menopause, slow bleeding from the stomach or bowel is a common cause, and some causes, such as polyps or coeliac disease, need treatment of their own.
Can I give blood if I have iron deficiency?
Not until your iron levels have recovered and you’ve been checked. Frequent donation is itself a cause of low iron.
Is an iron infusion better than tablets?
It works faster, but tablets work well for most people and avoid a hospital visit. Infusions are used when tablets aren’t suitable or haven’t worked.
References
- Snook J, Bhala N, Beales ILP, et al. British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults. Gut 2021;70:2030–2051. https://gut.bmj.com/content/70/11/2030
- NICE. Suspected cancer: recognition and referral (NG12). Updated 2025. https://www.nice.org.uk/guidance/ng12
- NICE. Quantitative faecal immunochemical testing to guide colorectal cancer pathway referral in primary care (DG56). 2023. https://www.nice.org.uk/guidance/dg56
- NICE. Coeliac disease: recognition, assessment and management (NG20). 2015. https://www.nice.org.uk/guidance/ng20
- NICE Clinical Knowledge Summaries. Anaemia: iron deficiency. https://cks.nice.org.uk/topics/anaemia-iron-deficiency/
- Stoffel NU, Cercamondi CI, Brittenham G, et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women. Lancet Haematology 2017;4:e524–e533.
- NHS. Iron deficiency anaemia. https://www.nhs.uk/conditions/iron-deficiency-anaemia/