Low Ferritin
Ferritin is the protein that stores iron. A low ferritin is the most reliable sign that your iron stores are running out, often before you become anaemic. The fix is usually simple, but finding out why you’re low matters just as much. Treatment is covered in our iron deficiency fact sheet.
Quick answer: A ferritin under 30 µg/L means low iron stores in adults, and under 15 µg/L means they’re almost empty. Heavy periods, pregnancy, low-iron diets and blood donation are the usual causes. Men and women after menopause with iron deficiency usually need bowel and stomach checks, because hidden gut bleeding is possible.
What the test measures
Ferritin stores iron inside your cells, and the small amount in your blood mirrors those stores. It falls first when you run short of iron, often months before your haemoglobin drops and you become anaemic. It’s usually ordered as part of iron studies, with serum iron, transferrin and transferrin saturation.
The catch: ferritin is also an acute-phase protein, so it rises with inflammation, infection and liver disease. That can push a low ferritin up into the normal range and hide iron deficiency.
Typical adult cut-offs
- Under 15 µg/L: iron stores are essentially empty. This is very specific for iron deficiency.
- Under 30 µg/L: low iron stores. This is the cut-off most widely used in Australia and the UK, even if your haemoglobin is normal.
- 30–100 µg/L with inflammation (for example inflammatory bowel disease, kidney disease or a recent infection): iron deficiency is still possible. A transferrin saturation under 20% supports it.
- Over 150 µg/L: iron deficiency is unlikely, even with inflammation.
- µg/L is the same number as ng/mL, the unit used in the US. Some labs print a lower limit of 15–20 µg/L, so a result in the 20s may not be flagged even though it’s low.
- Anaemia (WHO): haemoglobin under 130 g/L (13.0 g/dL) in men and under 120 g/L (12.0 g/dL) in women who aren’t pregnant.
What a low result usually means
Common causes:
- Heavy periods, the commonest cause in women before menopause. See heavy periods.
- Pregnancy and breastfeeding, when iron needs rise sharply.
- A diet low in iron: vegetarian or vegan eating without planning, restrictive diets, or small appetites in older people.
- Regular blood donation.
- Growth spurts in teenagers, and endurance sport.
- Medicines: aspirin and anti-inflammatories (such as ibuprofen) can cause slow bleeding from the stomach, and long-term acid-reducing medicines reduce iron absorption.
Less common but important:
- Bowel or stomach cancer, which can bleed slowly without any visible blood.
- Coeliac disease, found in about 3–5% of people with unexplained iron-deficiency anaemia. See coeliac disease.
- Stomach ulcers, inflammatory bowel disease and Helicobacter pylori infection.
- Weight-loss (bariatric) surgery and other stomach or bowel surgery.
- Blood loss in the urine, which can come from the kidneys or bladder.
Symptoms
- Often none, especially early on.
- Tiredness, poor concentration, headaches, and breathlessness or a racing heart on exertion.
- Restless legs, hair shedding, brittle or spoon-shaped nails, and a sore tongue.
- Craving ice or non-food items (pica).
- Pale skin once anaemia develops.
What happens next
- A full blood count to check for anaemia, and CRP if inflammation might be hiding a low ferritin.
- Look for the cause: a history of periods, diet, medicines, blood donation and gut symptoms, a coeliac blood test for most people, and a urine test for blood.
- Men of any age and women after menopause with iron-deficiency anaemia are usually offered a gastroscopy and colonoscopy, as the British Society of Gastroenterology recommends. Younger women with heavy periods usually don’t need them unless there are red flags or a strong family history of bowel cancer.
- Treatment: iron tablets, often every second day, for about 3 months after haemoglobin returns to normal to refill stores. An iron infusion helps when tablets fail or aren’t tolerated.
- Repeat the blood test after 2–4 weeks if you’re anaemic, to check haemoglobin is rising, and again once the course is finished.
Get urgent help (000 in Australia, or your local emergency number) for chest pain, fainting, severe breathlessness, vomiting blood, or black or bloody bowel motions. See your GP within a week or two if you’re a man or past menopause with iron deficiency, or have unexplained weight loss, a change in bowel habit, ongoing tummy pain or trouble swallowing: the cause needs checking. See your GP soon if you’re pregnant with low iron, or still low after 3 months of tablets.
Practise reading results. Play Panelysis, the daily blood-test puzzle: a fictional patient, a real-looking panel, three guesses. More in medical games.
Common questions
What ferritin level is too low?
In adults, a ferritin under 30 µg/L (30 ng/mL) means low iron stores, and under 15 µg/L means they’re almost empty. If you have inflammation, iron deficiency is still possible with a ferritin up to about 100 µg/L, and your doctor will look at transferrin saturation too.
Can you have low ferritin without anaemia?
Yes. Ferritin falls before haemoglobin does, so many people have low iron stores with a normal blood count. This iron deficiency without anaemia can still cause tiredness and restless legs, and it’s worth treating and finding the cause.
Is a ferritin of 20 low?
Yes. A ferritin of 20 µg/L is below the 30 µg/L cut-off widely used for low iron stores, even though some labs don’t flag it. Your GP will usually suggest iron and look for the cause.
Can my ferritin be normal if I’m iron deficient?
Yes. Inflammation, infection, liver disease and kidney disease all raise ferritin, which can hide low iron. In those situations, a transferrin saturation under 20% or a ferritin under about 100 µg/L can still point to iron deficiency.
How long does it take to raise ferritin?
Haemoglobin usually starts rising within 2–4 weeks of starting iron tablets. Refilling iron stores takes longer: guidelines suggest continuing for about 3 months after haemoglobin is back to normal, then rechecking.
Why do I need a colonoscopy for low iron?
In men and in women after menopause, iron deficiency is often caused by slow bleeding from the gut that you can’t see, and a small number have bowel or stomach cancer. A gastroscopy and colonoscopy find the cause so it can be treated.
Should I take iron supplements without a blood test?
It’s better to test first. Iron can mask a slowly bleeding problem, isn’t needed if your stores are full, and can build up in people with haemochromatosis. Keep iron tablets away from children, as an overdose can be fatal.
Evidence and more information
- Pathology Tests Explained (RCPA): Ferritin
- Pathology Tests Explained (RCPA): Iron studies
- Snook et al, Gut 2021: British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults (ferritin cut-offs, coeliac, who needs endoscopy)
- Pasricha et al, Medical Journal of Australia 2010: Diagnosis and management of iron deficiency anaemia, a clinical update
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