Low Ferritin Levels & Symptoms

Low ferritin at a glance

Ferritin is the protein that stores iron inside your cells, mainly in the liver, spleen and bone marrow. A small amount leaks into the blood, and the level in the blood mirrors how much iron is in storage. That makes serum ferritin the single most useful blood test for iron deficiency: when ferritin is low, iron stores are low.

Key points about low ferritin:

• Under 15 ng/mL (µg/L) is the World Health Organization's threshold for iron deficiency in otherwise healthy adults – stores are essentially empty.
• Under 30 ng/mL is used by many laboratories and clinicians as a more sensitive threshold, because the 15 cut-off misses a substantial number of people with iron deficiency.
• Under 45 ng/mL is the threshold the American Gastroenterological Association (AGA) uses to diagnose iron deficiency in people who already have anaemia.
• Under 70 ng/mL is WHO's suggested threshold when infection or inflammation is present, because inflammation pushes ferritin up and can hide a deficiency.
• Low ferritin can cause symptoms – especially tiredness and reduced exercise tolerance – even before haemoglobin falls. This is called iron deficiency without anaemia.

The checker above applies these thresholds to your ferritin result (in ng/mL, µg/L or pmol/L), takes account of your sex and whether you have an inflammatory condition, and – if you add your haemoglobin – tells you whether there is also anaemia.

Ferritin levels chart

The usual laboratory reference interval is about 10–120 ng/mL for women and 20–250 ng/mL for men in the NBME reference values, but ranges vary considerably between laboratories – some print a lower limit as low as 10 or 12, which is below the level at which many experts would diagnose iron deficiency. A ferritin of 14 can therefore appear "normal" on one report and still mean empty stores. ng/mL and µg/L are the same number. To convert to pmol/L, multiply by 2.247; the ferritin converter does it for you.

Why different thresholds exist

Choosing a ferritin cut-off is a trade-off between sensitivity (catching everyone with iron deficiency) and specificity (not labelling people who are iron replete). The gold standard for iron stores is a bone-marrow iron stain, which is rarely done today. Studies comparing ferritin with marrow iron found that a cut-off of 15 ng/mL is very specific – almost everyone below it is iron deficient – but misses many people with deficiency. Raising the cut-off to 30 or 45 catches far more, at the cost of a few false positives.

The WHO guideline also uses a lower threshold of 12 µg/L for children under 5. Pregnancy has its own considerations because ferritin falls as iron is transferred to the baby.

Low ferritin symptoms

Symptoms of low ferritin are those of iron deficiency, which can occur with or without anaemia:

Many of these symptoms are common and have other causes, so they do not prove iron deficiency – but low ferritin with these symptoms is a combination worth discussing. A 2021 review in *Clinical Medicine* argued that iron deficiency without anaemia is under-recognised and can cause real symptoms that improve once it is corrected.

What causes low ferritin?

Iron deficiency happens when iron losses or needs exceed what the body absorbs.

Increased losses (the most common reason in adults)

• Heavy menstrual bleeding – the leading cause in women of reproductive age.
• Gastrointestinal blood loss – from ulcers, inflammation, polyps or bowel cancer; often invisible. This is why iron deficiency in men and post-menopausal women is always investigated.
• Frequent blood donation.
• Other bleeding – nosebleeds, blood in the urine, after surgery or childbirth.

Increased needs

• Pregnancy, especially in the second and third trimesters.
• Growth in infants, children and adolescents.
• Endurance exercise, which increases iron turnover and losses.

Reduced intake or absorption

• Diets low in iron, or relying on plant sources without attention to absorption.
• Coeliac disease – a common, often missed cause.
• Atrophic gastritis, Helicobacter pylori infection, previous gastric or bariatric surgery.
• Inflammatory bowel disease.
• Long-term use of acid-reducing medicines can reduce iron absorption in some people.

The AGA guideline recommends that men and post-menopausal women with iron-deficiency anaemia have bidirectional endoscopy (upper endoscopy and colonoscopy) and testing for coeliac disease, and it discusses individualised approaches in pre-menopausal women. That is a clinical decision, but it explains why your clinician may suggest these tests.

About the ferritin test

Ferritin is measured in a standard blood sample, often alongside a full blood count and an iron panel. No special preparation is usually needed, although some laboratories prefer a morning sample when serum iron and transferrin saturation are measured at the same time. Iron supplements do not distort ferritin as quickly as they distort serum iron, but an intravenous iron infusion raises ferritin sharply for several weeks, so testing too soon afterwards can be misleading. If you have had a recent infection, ferritin may be temporarily raised; a repeat test after you have recovered gives a truer picture. Results are reported in ng/mL in the US and µg/L elsewhere – the same number – and occasionally in pmol/L.

Ferritin and inflammation: the main trap

Ferritin is an acute-phase protein: it rises during infection, inflammation, liver injury, cancer, heavy alcohol use and metabolic syndrome, regardless of iron stores. That means:

• A low ferritin is reliable – it almost always means low iron stores.
• A normal or high ferritin does not rule out iron deficiency if inflammation is present.

In those situations, clinicians use additional tests:

Our TIBC blood test page calculates TSAT from your iron and TIBC and explains these patterns in detail.

Low ferritin with a normal haemoglobin

Ferritin falls first, then transferrin saturation, and only later haemoglobin and MCV. So a normal CBC does not exclude iron deficiency. The stages are often described as:

Recognising stage 1 or 2 gives an opportunity to find and address the cause before anaemia develops.

Low ferritin in specific groups

Pregnancy

Iron needs rise sharply during pregnancy to support the expanding blood volume, the placenta and the baby. Ferritin naturally falls as pregnancy progresses, and many people who start pregnancy with modest stores become iron deficient by the third trimester. Because haemoglobin is also diluted in pregnancy, WHO uses lower anaemia thresholds for pregnant women (11.0 g/dL in the first and third trimesters, 10.5 g/dL in the second). Maternity teams commonly check a blood count at booking and again later in pregnancy, and many also check ferritin. If your ferritin or haemoglobin is low during pregnancy, discuss it with your midwife or obstetrician rather than adjusting supplements on your own.

Women with heavy periods

Heavy menstrual bleeding is very common and often under-recognised, partly because people get used to their own normal. It is one of the main reasons young women have low ferritin. Clinicians may ask about the number of days of bleeding, how often protection needs changing, flooding and clots. Addressing heavy periods is often as important as replacing iron.

Athletes

Endurance athletes, especially runners and female athletes, have higher rates of low ferritin. Iron is lost in sweat and through the gut, the impact of running can break red cells in the feet, and hepcidin rises for a few hours after hard exercise, temporarily reducing absorption. Sports medicine clinicians sometimes use higher working thresholds for ferritin in athletes, but these are not universally agreed.

Blood donors

Each whole-blood donation removes roughly 200–250 mg of iron. Frequent donors – particularly young women and teenagers – are at risk of falling ferritin. Some blood services now check ferritin or recommend longer gaps between donations for this reason.

Children and teenagers

WHO uses a lower threshold of 12 µg/L for children under 5. Rapid growth in infancy and adolescence, and early menstruation in teenage girls, increase needs. Toddlers who drink large volumes of cow's milk are at particular risk, because milk is low in iron and can displace iron-rich foods.

Older adults

In older adults, low ferritin is less often dietary and more often due to blood loss from the gut or reduced absorption. It is investigated rather than simply treated.

Worked examples

• Woman, 29, ferritin 8 ng/mL, haemoglobin 12.6 g/dL: iron deficiency (under 15) without anaemia (Hb at or above 12.0). Common with heavy periods.
• Woman, 41, ferritin 22 ng/mL: low – iron deficiency likely by the 30 ng/mL threshold, even though some lab ranges would call it normal.
• Man, 63, ferritin 40 ng/mL, haemoglobin 11.4 g/dL: anaemia with ferritin under 45 – meets the AGA threshold for iron-deficiency anaemia, and the cause should be investigated.
• Adult with rheumatoid arthritis, ferritin 60 ng/mL: possible iron deficiency despite a "normal" ferritin, because of inflammation (WHO threshold 70). TSAT helps.

Raising ferritin: what is involved

Treatment of iron deficiency – including whether to use oral or intravenous iron, the dose, and how long – is a decision for you and your clinician, and it depends on the cause, how low your levels are, other conditions and how well you tolerate iron. It is important not to take iron without knowing you need it: excess iron is harmful, and supplements can mask a bleeding source that needs finding. General points that are widely accepted:

• Finding and treating the cause matters as much as replacing iron.
• Ferritin is usually rechecked after a period of treatment to confirm that stores are recovering.
• Haemoglobin usually starts to rise within a few weeks of effective treatment, while ferritin takes longer to rebuild.
• Food sources of iron include red meat, poultry, fish, legumes, tofu, fortified cereals and dark leafy greens. Haem iron from animal foods is absorbed more readily than non-haem iron from plants, and vitamin C taken with a meal increases non-haem iron absorption.

When to see a doctor

• Your ferritin is below 30 ng/mL, or below your lab's range, particularly with symptoms.
• You are a man or a post-menopausal woman with low ferritin – the cause needs looking for.
• You have black or bloody stools, unexplained weight loss, change in bowel habit or abdominal pain.
• You have very heavy periods – needing to change protection every hour or two, passing large clots, or bleeding for more than 7 days.
• You are pregnant and ferritin or haemoglobin is low.