Serum iron µg/dL to µmol/L Converter

Serum iron in two units: the short answer

To convert serum iron from µg/dL (mcg/dL) to µmol/L, multiply by 0.1791. To convert µmol/L back to µg/dL, multiply by 5.585 (or divide by 0.1791). A serum iron of 100 µg/dL is therefore 17.9 µmol/L, and 12 µmol/L is 67 µg/dL. The same factor applies to total iron-binding capacity (TIBC) and unsaturated iron-binding capacity (UIBC), which are also expressed as iron concentrations. The converter above handles both directions and shows a typical adult range.

Serum iron is one of the most misunderstood blood tests. It is part of the "iron studies" panel, but on its own it is a poor guide to whether a person is iron deficient or overloaded, because it swings widely from hour to hour and day to day. This guide explains how to convert serum iron and its companion tests, what they measure, how they fit together with ferritin and transferrin saturation, and why serum iron should rarely be interpreted alone.

What serum iron measures

Iron is essential for making hemoglobin, myoglobin and many enzymes. An adult body contains about 3–4 g of iron: roughly two-thirds in hemoglobin, about a quarter stored as ferritin and haemosiderin, and small amounts in muscle and enzymes. Only about 3–4 mg – a tiny fraction – is circulating in the blood at any time, bound to the transport protein transferrin.

The serum iron test measures this transferrin-bound iron. It reflects iron in transit between the gut, stores and the bone marrow, not the amount stored. Because about 20–25 mg of iron passes through the plasma each day – mostly recycled from old red cells – the circulating pool turns over several times daily, and the level can change quickly.

The iron studies panel

Serum iron is usually reported with:

• Transferrin – the transport protein itself, in mg/dL or g/L.
• TIBC (total iron-binding capacity) – the maximum amount of iron that the transferrin in the blood could carry, reported in µg/dL or µmol/L. It is an indirect measure of transferrin.
• UIBC (unsaturated iron-binding capacity) – the spare capacity: TIBC minus serum iron.
• Transferrin saturation (TSAT) – serum iron ÷ TIBC × 100%. It shows what proportion of transferrin's capacity is occupied.
• Ferritin – the best single test of iron stores.

Because serum iron and TIBC share the same unit, TSAT is the same whichever unit you use, as long as both are in the same unit. Our transferrin saturation calculator handles mixed units for you.

µg/dL and µmol/L explained

• µg/dL (micrograms per deciliter), also written mcg/dL – used in the United States.
• µmol/L (micromoles per liter) – the SI unit used in the UK, Europe, Australia and elsewhere.

Why the factor is 0.1791

Iron has an atomic mass of 55.845 g/mol. A concentration of 1 µg/dL is 10 µg per liter, which is 10 ÷ 55.845 = 0.1791 µmol/L. Conversely, 1 µmol/L = 5.585 µg/dL.

Transferrin in g/L and TIBC

When transferrin is measured directly, TIBC can be estimated from it. Each transferrin molecule carries two iron atoms, and the commonly used conversion is TIBC (µmol/L) ≈ transferrin (g/L) × 25.1, or TIBC (µg/dL) ≈ transferrin (mg/dL) × 1.40 (some laboratories use 1.25–1.43). Use your laboratory's stated method where available.

How to convert serum iron step by step

1. Check the unit and whether the value is serum iron, TIBC or UIBC.
2. For µg/dL to µmol/L, multiply by 0.1791.
3. For µmol/L to µg/dL, multiply by 5.585.
4. Round µmol/L to one decimal place and µg/dL to whole numbers.

Worked examples

• 40 µg/dL × 0.1791 = 7.2 µmol/L – low.
• 60 µg/dL × 0.1791 = 10.7 µmol/L – the lower end of a typical adult range.
• 120 µg/dL × 0.1791 = 21.5 µmol/L.
• 170 µg/dL × 0.1791 = 30.4 µmol/L – the upper end of a typical adult range.
• TIBC 350 µg/dL × 0.1791 = 62.7 µmol/L.
• 15 µmol/L × 5.585 = 84 µg/dL.
• TIBC 72 µmol/L × 5.585 = 402 µg/dL – raised, as often seen in iron deficiency.

Mental shortcut

Divide µg/dL by 5.6, or multiply µmol/L by 5.6. For 90 µg/dL: 90 ÷ 5.6 = 16.1 µmol/L (exact: 16.1).

Serum iron conversion chart

Normal ranges for serum iron and TIBC

Typical adult ranges (vary by laboratory and sex):

Men tend to have slightly higher serum iron and saturation than premenopausal women. Children have lower values, and newborns have high values that fall over the first months.

Why serum iron alone is unreliable

Serum iron is affected by many factors unrelated to body iron status:

• Daily rhythm – serum iron is typically highest in the morning and can fall by 30% or more by the evening.
• Day-to-day variation – within-person variation is about 25–30%, one of the highest of any common blood test.
• Meals and supplements – an iron tablet or iron-rich meal can raise serum iron sharply for several hours.
• Inflammation – infection, inflammation and cancer reduce serum iron within hours, through the hormone hepcidin, which locks iron in stores and blocks absorption.
• Menstruation – levels may be lower around periods.

So a low serum iron does not necessarily mean iron deficiency, and a normal one does not rule it out. That is why guidelines base the diagnosis of iron deficiency mainly on ferritin, supported by transferrin saturation, rather than serum iron.

Interpreting the iron panel as a whole

Typical patterns:

The combination of a low TSAT with a high TIBC and low ferritin is the classic picture of iron deficiency. A high fasting TSAT – especially above 45% – with a raised ferritin raises the possibility of haemochromatosis and usually prompts genetic testing.

Causes of low serum iron

• Iron deficiency – from blood loss (heavy periods, gut bleeding, frequent blood donation), low intake, increased needs (pregnancy, growth) or malabsorption (coeliac disease, after gastric surgery, atrophic gastritis, long-term acid-suppressing medicines).
• Inflammation and infection – acute or chronic.
• Chronic kidney disease.
• Cancer.
• Evening sampling or recent illness.

Causes of high serum iron

• Hereditary haemochromatosis.
• Repeated blood transfusions (transfusional iron overload).
• Excessive iron supplements or recent intravenous iron.
• Liver disease – damaged liver cells release iron and ferritin.
• Haemolytic anaemias and ineffective red cell production – such as thalassaemia and sideroblastic anaemia.
• Iron poisoning – accidental ingestion of iron tablets is a significant cause of poisoning in young children and requires emergency care.

Hepcidin: the iron "gatekeeper"

Much of the behaviour of serum iron is explained by hepcidin, a hormone made by the liver and discovered in 2000–2001. Hepcidin blocks ferroportin, the only known channel that lets iron out of gut cells and out of the macrophages that recycle old red cells. When hepcidin is high, iron absorption falls and iron is trapped in stores, so serum iron drops. When hepcidin is low, absorption increases and stored iron is released.

• Inflammation raises hepcidin within hours (via interleukin-6), which is why serum iron falls quickly during infection and why anaemia of inflammation develops despite normal stores.
• Iron deficiency and active red cell production lower hepcidin, increasing absorption.
• Haemochromatosis is caused by inappropriately low hepcidin, so iron is absorbed excessively even when stores are full.
• Oral iron doses raise hepcidin for about 24 hours, which is one reason once-daily or alternate-day dosing may be absorbed as efficiently as more frequent dosing.

Hepcidin can be measured in research settings but is not yet a routine clinical test.

Dietary iron and absorption

Iron in food comes in two forms:

• Heme iron – from meat, poultry and fish. About 15–35% is absorbed, and absorption is relatively unaffected by other foods.
• Non-heme iron – from plants, fortified cereals and supplements. Only about 2–20% is absorbed, and absorption depends strongly on other foods: vitamin C, meat and fish increase it; tea, coffee, calcium, phytates (in whole grains and legumes) and some polyphenols reduce it.

The US recommended dietary allowances are:

People following vegetarian diets are advised that their requirement may be about 1.8 times higher, because of lower absorption of non-heme iron. The adult tolerable upper intake level is 45 mg per day from all sources, unless a clinician prescribes more for deficiency.

Iron in pregnancy

Iron needs rise substantially in pregnancy to support the expanded blood volume, the placenta and the baby. Iron deficiency in pregnancy is linked to preterm birth, low birth weight and maternal fatigue and blood loss complications. Serum iron and TIBC change in pregnancy – TIBC rises because oestrogen increases transferrin – so ferritin is again the preferred test. Many antenatal services check ferritin in early pregnancy and recommend supplements when it is low.

How to get a reliable iron result

To reduce variation, many laboratories and clinicians recommend:

• a morning sample, ideally before 10 a.m.
• fasting overnight, particularly when assessing for iron overload
• not taking iron supplements for at least 24 hours before the test (longer after high doses)
• waiting at least four weeks after an intravenous iron infusion before rechecking iron studies
• avoiding testing during an acute infection where possible

What affects serum iron results

• Time of day, fasting and recent meals – see above.
• Oral contraceptives and pregnancy – raise transferrin and TIBC.
• Inflammation – lowers serum iron and TIBC.
• Haemolysis in the sample – releases iron from red cells and raises results.
• Iron dextran or other intravenous iron – can interfere with some assays for days.
• Malnutrition and liver disease – lower transferrin and TIBC.

Iron poisoning

Iron tablets are a leading cause of serious poisoning in young children, because adult iron supplements can look like sweets and a relatively small number of tablets can be dangerous. Toxicity is estimated from the amount of elemental iron swallowed per kilogram of body weight – generally, more than about 20 mg/kg may cause symptoms, and more than about 60 mg/kg can be life-threatening. Symptoms progress through stages: vomiting, diarrhoea and abdominal pain in the first hours, an apparent recovery, then shock, metabolic acidosis, liver failure and, weeks later, bowel scarring.

In poisoning, serum iron measured about four to six hours after ingestion helps guide treatment. A level above about 500 µg/dL (90 µmol/L) is generally associated with significant toxicity, and treatment with the chelating agent deferoxamine is considered. Anyone who may have swallowed an overdose of iron should be taken to emergency care immediately, without waiting for symptoms. Keeping supplements in child-resistant containers out of reach is the best prevention.

Comparing iron studies across laboratories

When results come from different countries, convert serum iron and TIBC into the same unit before calculating transferrin saturation. For example, a serum iron of 9 µmol/L from a UK laboratory with a TIBC of 380 µg/dL from a US laboratory would give a meaningless ratio if the units were not matched; converted, 380 µg/dL is 68 µmol/L, so TSAT ≈ 9 ÷ 68 = 13%. Ideally, serum iron and TIBC should come from the same sample, since serum iron changes so quickly.

When to see a doctor

See a doctor if your iron studies show a low ferritin or low transferrin saturation, particularly with tiredness, breathlessness, heavy periods or anaemia. Men and postmenopausal women with iron deficiency should be assessed for a cause such as bleeding from the gut. Also see a doctor if your fasting transferrin saturation is above 45% or your ferritin is high, especially with joint pains, fatigue, diabetes or abnormal liver tests, or a family history of haemochromatosis. Seek emergency care immediately if a child may have swallowed iron tablets.