Ferritin ng/mL to pmol/L Converter

Ferritin in two units: the short answer

Ferritin is one of the few tests where the two most common units give the same number. 1 ng/mL equals 1 µg/L, so a ferritin of 45 ng/mL is exactly 45 µg/L – no conversion is needed. The molar unit is different: to convert ng/mL (or µg/L) to pmol/L, multiply by 2.247; to go back, divide by 2.247. A ferritin of 30 ng/mL is therefore 67 pmol/L. The converter above handles the ng/mL ↔ pmol/L conversion and shows where a value falls against the thresholds used for iron deficiency.

Most laboratories worldwide report ferritin in ng/mL or µg/L, and only a minority use pmol/L, but the molar figure appears in some European reports and research papers. Much more important than the unit is understanding what ferritin does and does not tell you – because ferritin is both the best single test for iron deficiency and a test that inflammation can make look falsely reassuring.

What ferritin is

Ferritin is a protein that stores iron inside cells, mainly in the liver, spleen and bone marrow. Each ferritin molecule is a hollow shell that can hold up to about 4,500 iron atoms in a safe, non-toxic form. A small amount of ferritin leaks into the blood, and in healthy people the amount in the blood is proportional to the amount of iron stored in the body: roughly, 1 ng/mL of serum ferritin corresponds to about 8–10 mg of stored iron in an adult.

That proportionality is why a low ferritin is so useful: a low ferritin always means low iron stores. No other condition makes ferritin falsely low.

The reverse is not true. Ferritin is also an acute-phase reactant – its production rises during inflammation, infection, cancer, liver damage and other illnesses, regardless of iron stores. So a normal or high ferritin does not rule out iron deficiency in someone who is unwell.

ng/mL, µg/L and pmol/L explained

• ng/mL (nanograms per milliliter) – the most common unit, especially in the United States.
• µg/L (micrograms per liter) – numerically identical to ng/mL, used in the UK, Australia and much of Europe.
• pmol/L (picomoles per liter) – a molar unit used by a minority of laboratories.

Why the factor is 2.247

Ferritin is a large protein complex. For unit conversion, laboratories use a molar mass of about 445,000 g/mol for apoferritin (the iron-free protein shell). A concentration of 1 ng/mL is 1,000,000 pg per liter; dividing by 445,000 pg/pmol gives 2.247 pmol/L. Because the true molar mass varies with iron content, the molar unit is a convention rather than an exact count of molecules – one reason most laboratories prefer mass units.

How to convert ferritin step by step

1. If your report is in ng/mL and you need µg/L (or the other way), the number stays the same.
2. To convert ng/mL or µg/L to pmol/L, multiply by 2.247.
3. To convert pmol/L to ng/mL, divide by 2.247.
4. Round to whole numbers; ferritin assays vary by several percent between methods.

Worked examples

• 15 ng/mL = 15 µg/L = 34 pmol/L – the WHO threshold for depleted iron stores in adults.
• 30 ng/mL = 30 µg/L = 67 pmol/L – a commonly used cut-off for iron deficiency.
• 45 ng/mL = 101 pmol/L – the American Gastroenterological Association threshold.
• 100 ng/mL = 225 pmol/L – the cut-off for iron deficiency in people with inflammation or chronic kidney disease in some guidelines.
• 500 pmol/L ÷ 2.247 = 223 ng/mL.
• 1,000 ng/mL = 2,247 pmol/L – a level that prompts investigation of iron overload or other causes.

Ferritin conversion chart

Ferritin levels: what the numbers mean

Laboratory reference ranges

Typical reference ranges are about 24–336 ng/mL (54–755 pmol/L) for adult men and 11–307 ng/mL (25–690 pmol/L) for adult women. These ranges are wide and their lower limits are often too low to be useful for detecting iron deficiency, because the reference population includes people with undiagnosed deficiency. Many experts recommend using clinical thresholds instead of the laboratory's lower limit.

Thresholds for iron deficiency

Different organisations use different cut-offs, and the trend over the last decade has been towards higher thresholds:

• Below 15 ng/mL (34 pmol/L) – the World Health Organization's 2020 threshold for iron deficiency in apparently healthy adults (below 12 ng/mL in children under five). At this level iron stores are essentially exhausted.
• Below 30 ng/mL (67 pmol/L) – widely used in clinical practice, including by the British Society of Gastroenterology and many haematology services. It identifies iron deficiency with much better sensitivity than 15 ng/mL.
• Below 45 ng/mL (101 pmol/L) – the American Gastroenterological Association recommends this cut-off in people with anaemia when evaluating for iron deficiency, to avoid missing cases.
• Below 70 ng/mL (157 pmol/L) – WHO's threshold in people with infection or inflammation.
• Below 100 ng/mL (225 pmol/L), or 100–299 ng/mL with transferrin saturation below 20% – the definition of iron deficiency used in heart failure guidelines (European Society of Cardiology), where IV iron improves symptoms.

Children and pregnancy

In children, ferritin is lower than in adults, and WHO uses below 12 ng/mL (27 pmol/L) for children under five and below 15 ng/mL for older children when there is no inflammation. In pregnancy, ferritin falls progressively as iron is transferred to the baby and red cell production increases; a ferritin below 30 ng/mL in pregnancy usually indicates the need for iron supplementation, and many antenatal guidelines screen for this in the first trimester.

High ferritin

A ferritin above the reference range is common, and the most frequent causes are not iron overload:

• Inflammation and infection – rheumatoid arthritis, inflammatory bowel disease, recent infections including COVID-19.
• Metabolic syndrome and fatty liver disease – one of the most common reasons for a moderately raised ferritin (often 300–1,000 ng/mL).
• Alcohol – regular heavy drinking raises ferritin.
• Liver disease – hepatitis and other causes of liver cell damage release ferritin.
• Cancer and some blood disorders.
• Kidney disease.
• Iron overload – hereditary haemochromatosis (most often from two copies of the HFE C282Y variant), repeated blood transfusions, or excessive iron supplements.

The key additional test is transferrin saturation (TSAT). A raised ferritin with a normal TSAT points towards inflammation, metabolic causes or alcohol. A raised ferritin with a fasting TSAT above about 45% suggests true iron overload and usually leads to HFE genetic testing.

Very high levels – above 1,000 ng/mL (2,247 pmol/L) – raise the risk of liver damage when due to iron overload, and when extremely high (for example above 10,000 ng/mL) can point to rare inflammatory conditions such as haemophagocytic lymphohistiocytosis or adult-onset Still's disease.

Ferritin and the rest of the iron panel

Ferritin is usually ordered with other iron tests, and each adds something:

When iron deficiency and inflammation coexist – common in chronic disease – ferritin may be "normal" while TSAT is low. Our transferrin saturation calculator can help with that part of the picture.

Iron deficiency without anaemia

Iron stores are used up before haemoglobin falls. A person can therefore have a low ferritin with a normal haemoglobin, a stage called iron deficiency without anaemia. It can still cause fatigue, reduced exercise capacity, hair shedding, restless legs and difficulty concentrating, and treating it can improve symptoms in some people. Restless legs syndrome guidelines, for example, recommend iron treatment when ferritin is below about 75 ng/mL.

Treating low ferritin and checking the response

When iron deficiency is confirmed, the cause should be identified as well as treated. Oral iron is the usual first step. Current evidence suggests that taking iron once daily or on alternate days may be absorbed as well as, or better than, several doses a day, because each dose raises the hormone hepcidin, which blocks iron absorption for roughly 24 hours. Taking iron with vitamin C or on an empty stomach improves absorption; tea, coffee, calcium and antacids reduce it.

A typical monitoring pattern is:

• Haemoglobin checked after about two to four weeks; a rise of about 1–2 g/dL (10–20 g/L) within four weeks shows a good response.
• Ferritin checked after about three months; many clinicians aim for at least 50–100 ng/mL to restore stores, then continue treatment for a further period.
• Intravenous iron is considered when oral iron is not tolerated, does not work, or when rapid repletion is needed (for example, late pregnancy, heart failure or before surgery).

Example: a woman with heavy periods has a ferritin of 9 µg/L in the UK (9 ng/mL, 20 pmol/L) and a haemoglobin of 105 g/L. After three months of iron, a US laboratory reports a ferritin of 38 ng/mL – the same as 38 µg/L. Her stores have improved but are still below the 50 ng/mL many clinicians aim for, so treatment would usually continue.

Ferritin in athletes and blood donors

Endurance athletes, particularly female runners, often have low ferritin. Sports medicine bodies commonly suggest that ferritin below about 30–35 ng/mL in an athlete is worth discussing, even with normal haemoglobin, because it may impair performance. Regular blood donors also lose about 200–250 mg of iron with each whole-blood donation; some blood services now measure ferritin in donors and recommend longer intervals or iron supplementation when it is low.

Haemochromatosis and ferritin

Hereditary haemochromatosis is one of the most common genetic conditions in people of Northern European descent: about 1 in 150–200 people carry two copies of the HFE C282Y variant. Not all of them develop iron overload, but those who do absorb too much iron from food over many years, which can damage the liver, pancreas, heart and joints.

Ferritin is used both to detect and to manage the condition:

• Detection. A raised ferritin together with a fasting transferrin saturation above about 45% leads to HFE genotyping. Family members of people with haemochromatosis are offered testing.
• Risk assessment. A ferritin above 1,000 µg/L (2,247 pmol/L) at diagnosis is associated with a higher risk of liver scarring, and further assessment of the liver is usually recommended.
• Treatment. Regular removal of blood (venesection or phlebotomy) lowers iron stores. Ferritin is checked periodically, with a common maintenance target of around 50–100 µg/L.

Because ferritin is often raised for other reasons, especially fatty liver disease and alcohol, a high ferritin alone is not enough to diagnose iron overload.

What affects ferritin results

• Inflammation and infection, even mild or recent, raise ferritin for weeks.
• Iron supplements or infusions raise ferritin; after an IV iron infusion, wait at least four weeks before rechecking, because levels can be temporarily very high.
• Menstrual blood loss, pregnancy, blood donation and gut bleeding lower stores.
• Diet – vegetarian and vegan diets are associated with lower stores, although not necessarily deficiency.
• Endurance exercise can lower ferritin through small losses in sweat, urine and the gut, and through hepcidin effects.
• Alcohol and fatty liver raise ferritin.
• Laboratory method – ferritin assays are standardised against WHO reference material, but results can still differ between laboratories by 10% or more.

When to see a doctor

See a doctor if your ferritin is below 30 ng/mL (67 pmol/L), especially with tiredness, breathlessness, heavy periods or a low haemoglobin. Iron deficiency in men and in women after menopause should always be investigated for a cause, particularly bleeding from the gut, so do not simply take supplements without assessment. Also see a doctor if ferritin is above about 300 ng/mL in men or 200 ng/mL in women on repeat testing, particularly with a high transferrin saturation, joint pains, diabetes or abnormal liver tests, or a family history of haemochromatosis.