Ferritin levels: the normal range, what low ferritin means, and when to see your GP

What ferritin is

Ferritin is a protein your cells use to store iron for later. A little of it circulates in your blood. WHO recommends using the ferritin level to assess iron stores in otherwise healthy people.

How ferritin differs from haemoglobin:

• haemoglobin shows how much iron is already at work in your red blood cells;
• ferritin shows how much iron is left in reserve.

Stores run down before haemoglobin falls. That’s why ferritin can be low while your full blood count looks normal.

Reports use µg/L or ng/mL. They’re the same thing: 20 µg/L equals 20 ng/mL, so there’s nothing to convert.

Tests done alongside ferritin

Ferritin alone doesn’t give the full picture. Your GP usually reads it with other results:

• full blood count: haemoglobin and red cell size. WHO defines anaemia as haemoglobin below 130 g/L in men and below 120 g/L in women who aren’t pregnant;
• C-reactive protein (CRP): to check for inflammation that pushes ferritin up;
• sometimes transferrin saturation, if the ferritin result is unclear.

Low ferritin with normal haemoglobin is iron deficiency without anaemia. When both are low, it’s iron deficiency anaemia.

Ferritin normal range: why labs print different numbers

The reference range on your report covers the results of most people tested by that lab. It depends on the method used and on who was included. So the lower limit on your report can sit below the cut-offs used in clinical guidelines.

Adult cut-offs from WHO (2020) and the British Society of Gastroenterology (BSG, 2021):

Treat the table as a guide, not a self-diagnosis tool. Your GP reads ferritin together with haemoglobin, symptoms and other tests. The scale below shows the same cut-offs: find where the number on your report falls.

Low ferritin: causes and iron deficiency symptoms

The NHS names these as the most common causes:

• heavy periods;
• pregnancy;
• bleeding from the stomach or gut: ulcers, inflammation, piles, ibuprofen or aspirin, and less often cancer;
• a diet low in iron.

Symptoms of iron deficiency include tiredness, breathlessness, a racing or noticeable heartbeat, pale skin and headaches. Less common are tinnitus, changes in taste, spoon-shaped nails, hair loss, cravings for non-food items and restless legs.

No single symptom confirms low iron. Tiredness also comes with poor sleep, thyroid problems or low mood, so rely on the test rather than on how you feel.

Ferritin and inflammation: why a normal result can mislead

Ferritin is an acute-phase protein: it rises with infection and inflammation, whatever your iron stores. Someone who is iron deficient can get a normal ferritin if tested during a cold or with a long-term inflammatory condition.

In 2020 WHO suggested that, with inflammation, ferritin below 30 µg/L in children and below 70 µg/L in adults may indicate iron deficiency. To check for inflammation, labs measure C-reactive protein (CRP) alongside ferritin. WHO treats CRP above 5 mg/L as raised.

The BSG adds that ferritin above 150 µg/L is unlikely with true iron deficiency, even with inflammation.

Had the blood test a week after flu? Ask your GP whether to repeat it once you’ve fully recovered.

High ferritin

High ferritin is a reason to find the cause, not to start iron. Common explanations are:

• inflammation or infection;
• iron build-up, including haemochromatosis.

Haemochromatosis is an inherited condition in which the body stores too much iron over many years. The NHS says it mostly affects people of white northern European descent and is especially common in Ireland, Scotland and Wales. Symptoms usually start between 30 and 60: constant tiredness, weakness and joint pain. Untreated, excess iron can damage the liver, joints, pancreas and heart. People with haemochromatosis should avoid iron and vitamin C supplements.

When to see your GP

See your GP if:

• you have symptoms of anaemia, such as breathlessness, a racing heartbeat or marked tiredness;
• your ferritin is below the lab range or below 30 µg/L;
• you’re a man or a woman after the menopause with iron deficiency: the BSG recommends checking the stomach and bowel;
• you’re pregnant or planning a pregnancy;
• your ferritin is above 150–200 µg/L;
• you notice signs of bleeding, or black stools when you’re not taking iron.

Who shouldn’t take iron without medical advice

Don’t start iron supplements on your own if you have:

• high ferritin, or haemochromatosis in the family;
• liver disease;
• a pregnancy: your midwife or GP sets the dose (see our pregnancy vitamins guide);
• prescriptions for levothyroxine, levodopa or stomach-acid reducers: iron interacts with them.

Children should only take iron on a doctor’s advice. Accidental iron poisoning is dangerous for children under 6.

After the test: supplements only on medical advice

If your GP confirms deficiency, they’ll choose the form, dose and duration. The BSG guideline suggests starting with one tablet a day (50–100 mg of elemental iron), or one every other day if it isn’t tolerated. Treatment continues for about 3 months after haemoglobin returns to normal. Your GP may repeat a blood test within a few weeks to check it’s working.

We compare the forms, elemental iron per tablet and how to take them in our guide to iron tablets and the best iron supplement. Other common tests are collected in tests and deficiencies, and the vitamin D test guide explains 25(OH)D results.

How to choose iron on iHerb if your GP advises it

1. Make sure you have clear advice: the form, the dose of elemental iron and the duration.
2. Check the “Iron (as …)” line on the label: it gives elemental iron.
3. If you were prescribed ferrous sulphate and it disagrees with you, ask about switching to bisglycinate.
4. Don’t double up: check your multivitamin and any supplements for women you already take.
5. Have follow-up blood tests when your GP asks.
6. Store the bottle where children can’t reach it.