If you have been waking up tired for weeks, brushing more hair off your shoulders than usual, or finding it harder to concentrate, and a recent blood test came back “normal”, low iron stores are one possible explanation worth checking. The marker for iron stores is called ferritin, and it is not always part of a basic blood test.

A full blood count (FBC) measures haemoglobin, the protein in red blood cells that carries oxygen. It does not measure how much iron your body holds in reserve. Iron stores can run low before haemoglobin falls far enough to count as anaemia, so a normal full blood count does not rule out low ferritin.

This article explains what low ferritin can feel like, what counts as low, what causes it, and when to speak to a doctor. A blood test gives information and is not a diagnosis: your GP or a doctor reviewing your result decides what it means for you.

What does low ferritin feel like?

Ferritin is the protein that stores iron, so a low ferritin means low iron stores. When iron is low enough to cause anaemia, the NHS lists these as the main symptoms of iron deficiency anaemia:

  • Tiredness and lack of energy.
  • Shortness of breath.
  • Noticeable heartbeats (palpitations).
  • Paler than usual skin.
  • Headaches.

The NHS also lists less common symptoms: hair loss, a sore tongue, mouth ulcers, itching, restless legs, nail changes such as spoon-shaped nails, tinnitus, an altered sense of taste, trouble swallowing, and pica, which is a craving to eat things that are not food.

People with low ferritin and no anaemia may describe a similar pattern, most often tiredness and hair shedding. None of these symptoms is specific. They overlap with thyroid problems, low vitamin D or B12, poor sleep, low mood and many other causes, which is why a blood test, rather than a symptom list, is how you find out. You do not need all of them, and having several does not prove your ferritin is low.

Low ferritin symptoms in women

Women are more likely than men to have low iron stores. The British Society of Gastroenterology (BSG) guideline notes that menstrual loss is commonly the cause of iron deficiency anaemia in women before the menopause, and the NHS lists heavy periods and pregnancy as very common causes. In pregnancy, the NHS says iron deficiency anaemia is most often caused by too little iron in the diet, so mention tiredness to your midwife rather than waiting.

The symptoms are the same as those above. If your periods are heavy, that is worth raising with your GP in its own right, because treating the iron without looking at the bleeding can leave the cause in place.

Low ferritin and hair shedding

Diffuse shedding across the whole scalp, rather than in patches, is the pattern called telogen effluvium. The British Association of Dermatologists (BAD) says telogen effluvium can come back if an underlying cause such as iron deficiency is not treated, and that a blood test may be done to check for causes such as thyroid conditions and iron deficiency. The shedding phase typically lasts 3 to 6 months, and BAD notes that it can take many months for hair to return to its normal volume and thickness.

Hair specialists disagree about how high ferritin needs to be for healthy hair growth. Some aim for a ferritin above 70 µg/L when shedding is active. That figure is specialist opinion, not a NICE threshold, and the evidence is limited, so treat it as context rather than a target. Our guides to hair loss blood tests and female hair loss blood tests cover the other markers that matter.

Low ferritin and brain fog

Many people describe brain fog or trouble concentrating alongside tiredness. It is not on the NHS symptom list for iron deficiency anaemia, and it has many other causes, including poor sleep, low mood, an underactive thyroid and low B12. Treat it as a reason to test several markers together, not as a sign of low ferritin by itself. Our brain fog guide and our article on being tired despite sleep set out what else a blood test can look at.

What counts as low ferritin?

There is no single UK cut-off, because laboratories set their own reference ranges. These are the thresholds used in UK guidance, which your doctor reads alongside your symptoms and the rest of your results:

  • Below 15 µg/L: indicates absent iron stores (BSG 2021).
  • Below 30 µg/L: generally indicates low body iron stores. NICE CKS uses 30 µg/L as its threshold for iron deficiency.
  • 30 to 45 µg/L: borderline. The BSG guideline suggests 45 µg/L as the best trade-off between sensitivity and specificity in practice, so a result in this band, particularly with symptoms, anaemia or inflammation, deserves a clinician’s attention even if the lab does not flag it.
  • Above 150 µg/L: iron deficiency is unlikely, even when inflammation is present (BSG 2021).

Most UK laboratories set their lower limit somewhere between 15 and 30 µg/L, and their upper limit varies with the laboratory, sex and age, so a result can be marked “normal” on your report and still sit in the borderline band. Always compare your result with the range printed on your own report. The units µg/L and ng/mL are numerically the same. You can read the full table on our ferritin blood test page.

Ferritin is also an acute-phase protein, which means infection or inflammation can push it up and hide low stores. That is one reason it is read together with other markers.

Low ferritin with normal iron or haemoglobin

It is possible to have low ferritin while your haemoglobin and serum iron look normal. Anaemia is defined by haemoglobin, below 130 g/L in men and below 120 g/L in non-pregnant women (WHO criteria, quoted in the BSG guideline), and haemoglobin can stay above those lines while stores are running down. Serum iron is a poor stand-alone measure because it changes through the day and with recent meals or supplements.

This is why doctors look at several markers together: ferritin for stores, a full blood count for haemoglobin and red cell size, and TIBC and transferrin saturation for how much iron is available to the body. A CRP can help show whether inflammation is raising ferritin. The ferritin and TIBC pair guide explains how the two are read together.

What causes low ferritin?

Low iron stores happen when iron going out, or needed, exceeds iron coming in. The recognised causes include:

  • Blood loss. Heavy periods are the commonest cause in women before the menopause. Blood donation is a recognised cause (BSG). Bleeding in the stomach or bowel, for example from ulcers, piles, inflammation of the gut, or anti-inflammatory painkillers such as ibuprofen and aspirin, can cause slow iron loss that you do not see (NHS).
  • Not enough iron in the diet. The NHS lists red meat, beans, pulses, nuts, dried fruit, fortified breakfast cereals and leafy green vegetables among the good sources. Tea, coffee, milk and dairy foods, and foods high in phytic acid such as wholegrain cereals, reduce how well you absorb iron from food and tablets.
  • Pregnancy. The NHS lists pregnancy as a very common cause of iron deficiency anaemia.
  • Problems absorbing iron. Coeliac disease and inflammatory bowel disease can both cause iron deficiency (the BSG guideline estimates about a third of people with active inflammatory bowel disease are iron deficient), and long-term acid-suppressing medicines such as proton pump inhibitors may contribute (BSG). Do not stop a prescribed medicine without speaking to your prescriber.

More than one factor often applies, and sometimes no cause is found. Finding the cause matters as much as correcting the number.

What a fuller check looks like

If you are investigating low iron properly, a single marker is rarely enough. A fuller check usually includes ferritin, a full blood count, and iron studies (serum iron, TIBC and transferrin saturation). Because the symptoms overlap, it often also includes vitamin D, vitamin B12 and thyroid function, which are other common contributors to tiredness and hair shedding.

Should you take iron tablets before you are tested?

Get tested first. Iron is not harmless in excess. The NHS says that taking 17 mg or less of iron a day from supplements is unlikely to cause harm, that doses above 20 mg a day can cause constipation, sickness and stomach pain, and that very high doses can be fatal, particularly to children, so tablets must be kept out of their reach. Extra iron will not help symptoms that have a different cause, and it can make the cause harder to find.

If a doctor confirms iron deficiency, treatment is usually iron tablets together with a search for the cause. For adults, the BSG guideline recommends starting with one tablet a day of ferrous sulphate, fumarate or gluconate, or one tablet every other day if daily tablets cause side effects. It suggests checking haemoglobin about 4 weeks after starting, and continuing treatment for around 3 months after haemoglobin returns to normal so that stores are rebuilt. The NHS says people often need to take tablets for about 6 months, and lists constipation or diarrhoea, stomach pain, heartburn, sickness and dark stools as possible side effects. Taking tablets with or soon after food can help, and a drink of orange juice after a tablet may help absorption. Your GP decides the dose, the length of treatment and when to recheck.

When to see a GP

See your GP if you think you may have iron deficiency, or if tiredness, breathlessness or hair shedding persist. Speak to them sooner if:

  • Your periods are heavy or getting heavier.
  • You are a man, or a woman after the menopause, with low ferritin or anaemia. Unexplained iron deficiency anaemia in an adult over 50 is investigated by examining the gut (BSG 2021).
  • You notice black, tarry stools or blood in your stools.

Call 999 for chest pain, severe breathlessness or fainting. A private blood test does not replace NHS care: share your results with your GP, who can arrange treatment and any further tests.

Getting tested at WMG Health

Ferritin is measured in several of our panels. The Hair Loss Essentials panel, the Advanced Hair & Hormone Check and the General Wellness panel all include ferritin with iron studies, and ferritin can also be added to a custom panel. Panels that include iron studies need a fast of at least 12 hours beforehand (water is fine), and you should not take iron tablets or supplements for 24 hours before your appointment. A morning appointment between 8am and 10am is preferred. Follow the instructions for the specific panel you book.

Results are released as each marker is reviewed by a GMC-registered doctor, and we confirm the expected timeframe when you book. No GP referral is required.

Common questions

What are the symptoms of low ferritin in women? The same as for everyone: tiredness, shortness of breath, palpitations, paler skin and headaches when iron is low enough to cause anaemia, with hair loss, restless legs, a sore tongue and nail changes among the less common signs. Heavy periods are the commonest cause in women before the menopause, so mention them to your GP.

What is a normal ferritin level? It depends on the laboratory, so use the range on your own report. Most UK laboratories set the lower limit between 15 and 30 µg/L. UK guidance treats a ferritin below 30 µg/L as indicating low iron stores, and a result between 30 and 45 µg/L is borderline.

Can ferritin be low when my haemoglobin is normal? Yes. Iron stores can be depleted before haemoglobin falls below the anaemia threshold, which is why a normal full blood count does not rule out low ferritin.

Can low ferritin cause hair loss? The British Association of Dermatologists says telogen effluvium (diffuse hair shedding) can come back if an underlying cause such as iron deficiency is not treated. Iron is one of several possible causes, along with thyroid problems, illness, stress and some medicines, so it is checked alongside other markers.

Can low ferritin cause brain fog? Some people with low iron stores report poor concentration, but brain fog is not on the NHS symptom list for iron deficiency anaemia and has many other causes. A blood test that checks iron, thyroid, vitamin D and B12 together is more informative than testing one marker.

Do I need to fast for a ferritin test? Ferritin on its own does not need fasting. The panels that include iron studies, such as Hair Loss Essentials and General Wellness, need a fast of at least 12 hours, so follow the instructions for the panel you book.

Do I need a GP referral for a ferritin test? No. WMG Health is direct-access, so you can book online or by phone on 020 3239 3378. We recommend sharing your results with your GP.

Sources

  • NHS: Iron deficiency anaemia, including the symptoms and treatment pages. nhs.uk/conditions/iron-deficiency-anaemia/
  • NHS: Iron (vitamins and minerals). nhs.uk/conditions/vitamins-and-minerals/iron/
  • Snook J et al. British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults. Gut 2021;70:2030 to 2051. doi:10.1136/gutjnl-2021-325210
  • NICE Clinical Knowledge Summaries: Anaemia, iron deficiency. cks.nice.org.uk/topics/anaemia-iron-deficiency/
  • British Association of Dermatologists: Telogen effluvium patient information leaflet. bad.org.uk/pils/telogen-effluvium/

This article is for general information only and does not constitute clinical advice. If you have concerns about your symptoms, speak to your GP.