Transferrin Saturation Calculator

Transferrin saturation in brief

Transferrin is the protein that carries iron in the blood. Transferrin saturation (TSAT) tells you what percentage of transferrin's iron-binding sites are occupied. It is calculated from two results in a standard iron panel:

TSAT (%) = serum iron ÷ total iron-binding capacity (TIBC) × 100

Both values must use the same unit – either µg/dL or µmol/L (1 µmol/L = 5.585 µg/dL). The calculator above accepts either and checks that iron is not higher than TIBC, which would suggest a unit mix-up.

Typical interpretation:

• below 20% – low; supports iron deficiency, especially with a low ferritin, but also occurs with inflammation
• 20–45% – typical
• above 45% – raised; the usual trigger for further tests for iron overload, such as haemochromatosis

TSAT is most useful when read together with ferritin, which reflects iron stores. Low TSAT with low ferritin points to iron deficiency; high TSAT with high ferritin raises the possibility of iron overload.

Worked examples

Because the ratio is unit-free, 7.2 ÷ 80.6 µmol/L gives the same 8.9% as 40 ÷ 450 µg/dL.

Step by step

1. Find serum iron and TIBC on your report and check that they use the same unit.
2. Divide serum iron by TIBC.
3. Multiply by 100 to get a percentage.
4. Compare with the range on your report, and look at ferritin at the same time.

If serum iron is in µmol/L and TIBC in µg/dL, convert one of them first by multiplying or dividing by 5.585. Mixing units is the most common error in calculating TSAT by hand.

Calculating TIBC from transferrin

Some laboratories report transferrin in g/L or mg/dL rather than TIBC. Each transferrin molecule binds two iron atoms, so TIBC can be estimated:

• TIBC (µmol/L) ≈ transferrin (g/L) × 25.1
• TIBC (µg/dL) ≈ transferrin (mg/dL) × 1.4 (approximately; factors between 1.25 and 1.43 are used)

For transferrin 2.5 g/L, TIBC ≈ 62.8 µmol/L. With serum iron 15 µmol/L, TSAT ≈ 24%. Some laboratories also report unsaturated iron-binding capacity (UIBC); TIBC = serum iron + UIBC.

How iron moves through the body

The body contains about 3–4 grams of iron. Most is in haemoglobin in red blood cells; the rest is stored as ferritin in the liver, spleen and bone marrow, or found in muscle and enzymes. Only a tiny amount – about 3 mg – is bound to transferrin in the blood at any moment, but this pool turns over many times a day as iron is delivered to the bone marrow and recycled from old red cells.

The hormone hepcidin, made by the liver, controls iron levels. It blocks iron absorption from the gut and iron release from stores. Hepcidin rises with inflammation and high iron, and falls with iron deficiency and increased red-cell production. This explains why TSAT is low in both iron deficiency (too little iron) and inflammation (iron locked away).

The iron panel: putting results together

Iron deficiency

Iron deficiency is the most common nutritional deficiency worldwide. TSAT below 20% supports the diagnosis, and values below about 16% are often used in research definitions. Ferritin is the most specific test: a ferritin below about 30 µg/L (ng/mL) strongly suggests iron deficiency in adults. Common causes include menstrual blood loss, pregnancy, gastrointestinal bleeding, low dietary intake, coeliac disease and other causes of malabsorption, and frequent blood donation.

Anaemia of inflammation

In chronic infections, autoimmune diseases, cancer, chronic kidney disease and obesity, hepcidin rises and iron is trapped in stores. Serum iron and TSAT fall, but ferritin is normal or high, because ferritin also rises with inflammation. Distinguishing inflammation from true iron deficiency can be difficult, and TSAT combined with ferritin, C-reactive protein and sometimes the soluble transferrin receptor helps.

Iron overload

A fasting TSAT above 45% is the usual threshold for suspecting iron overload. The most common cause in people of Northern European ancestry is HFE haemochromatosis, an inherited condition in which people who are homozygous for the C282Y variant absorb too much iron. Not everyone with the genotype develops iron overload, and men are affected more often and earlier than women, because menstruation and pregnancy remove iron. The 2022 European Association for the Study of the Liver (EASL) guideline recommends HFE genotyping in people with raised TSAT and raised ferritin. Other causes of high TSAT include repeated blood transfusions, some anaemias with ineffective red-cell production, liver disease and excessive iron supplementation.

Symptoms to be aware of

Iron deficiency

Iron deficiency develops gradually, and symptoms may not appear until anaemia is present. They include tiredness and lack of energy, breathlessness on exertion, pale skin, headaches, a fast or pounding heartbeat, brittle nails, hair thinning, a sore tongue, cracks at the corners of the mouth, restless legs and cravings for ice or non-food items (pica). In children, iron deficiency can affect growth and development. Many people, particularly women with heavy periods, have iron deficiency without anaemia, which can still cause fatigue and reduced exercise capacity.

Iron overload

Early haemochromatosis is often silent. As iron accumulates over years, it can cause fatigue, joint pain (classically in the knuckles of the index and middle fingers), abdominal pain, reduced libido or erectile dysfunction, skin darkening, diabetes, liver enlargement and, eventually, cirrhosis, liver cancer or heart failure. Early diagnosis through raised TSAT and ferritin – often found incidentally – allows treatment before organ damage occurs.

Reference ranges by age and sex

Serum iron and TIBC ranges are roughly: serum iron 60–170 µg/dL (10.7–30.4 µmol/L) and TIBC 250–450 µg/dL (44.8–80.6 µmol/L), varying by laboratory.

Factors that affect transferrin saturation

• Time of day: serum iron is higher in the morning and falls in the afternoon and evening, so morning samples are preferred.
• Meals and supplements: eating or taking iron raises serum iron for several hours; for overload screening, a fasting sample is recommended, and iron supplements are usually stopped for at least 24 hours beforehand.
• Inflammation: lowers serum iron and TSAT.
• Oral contraceptives and pregnancy: raise transferrin and TIBC, lowering TSAT.
• Liver disease: can lower transferrin production and raise ferritin.
• Malnutrition: lowers transferrin.
• Recent blood transfusion or iron infusion: temporarily raises serum iron and TSAT.

Because serum iron varies considerably from day to day – by 30% or more – a single abnormal TSAT should be repeated before drawing conclusions, ideally as a fasting morning sample.

TSAT in specific conditions

Heart failure

Iron deficiency is common in heart failure and is associated with worse symptoms and outcomes, even without anaemia. The 2021 European Society of Cardiology heart failure guidelines define iron deficiency as ferritin below 100 ng/mL, or ferritin 100–299 ng/mL with TSAT below 20%, and recommend periodic screening. Intravenous iron improves symptoms and quality of life in people with heart failure with reduced ejection fraction and iron deficiency.

Chronic kidney disease

In CKD, iron deficiency and anaemia of inflammation often coexist. The KDIGO anaemia guideline suggests a trial of iron in adults with CKD and anaemia when TSAT is 30% or less and ferritin is 500 ng/mL or less, if an increase in haemoglobin or a reduction in medicine doses is desired. People on dialysis are monitored regularly.

Pregnancy

Iron needs rise substantially during pregnancy. Ferritin is the main screening test, but TSAT can help when ferritin is difficult to interpret. Iron deficiency in pregnancy is associated with fatigue, a higher risk of needing a blood transfusion after birth, and possibly effects on the baby's development.

Iron in the diet

Dietary iron comes in two forms. Haem iron, found in red meat, poultry and fish, is absorbed well – about 15–35%. Non-haem iron, found in legumes, leafy greens, fortified cereals, tofu, nuts and seeds, is absorbed less efficiently – typically 2–20% – and absorption depends on what else is eaten:

• Vitamin C (citrus fruit, peppers, tomatoes) increases non-haem iron absorption when eaten at the same meal.
• Tea, coffee, calcium and phytates (in whole grains and legumes) reduce absorption; drinking tea or coffee between meals rather than with them can help.

Adult men need about 8–9 mg of iron a day, and menstruating women about 15–18 mg. Pregnant women need more – 27 mg a day in US recommendations. Vegetarians and vegans can meet their needs with careful planning, although US guidance suggests their requirement may be up to 1.8 times higher because of lower absorption.

Iron in athletes and blood donors

Endurance athletes, especially female runners, are at higher risk of iron deficiency because of increased losses through sweat, the gut and the breakdown of red cells from foot strike, combined with increased demand. Regular blood donors also lose iron – each whole-blood donation removes about 200–250 mg. Some blood services now measure ferritin in donors and recommend iron supplements or longer intervals between donations. For people with haemochromatosis, donating blood can be part of maintenance treatment where services allow it.

Interpreting an iron panel: two examples

Example 1. A 34-year-old woman with heavy periods feels tired. Her results: haemoglobin 10.8 g/dL, serum iron 35 µg/dL, TIBC 430 µg/dL and ferritin 8 ng/mL. TSAT is 35 ÷ 430 × 100 = 8%. The low TSAT, high TIBC and very low ferritin confirm iron deficiency anaemia. Her clinician would treat with iron, address the heavy periods and check that haemoglobin rises over the following weeks.

Example 2. A 48-year-old man has mildly raised liver enzymes on a routine check. A fasting iron panel shows serum iron 190 µg/dL, TIBC 250 µg/dL and ferritin 850 ng/mL. TSAT is 76%. The combination of high TSAT and high ferritin suggests iron overload, and HFE genotyping shows he is homozygous for C282Y. He starts regular venesection, and his liver enzymes normalise as ferritin falls.

Treatment depends on the cause

• Iron deficiency: find and treat the cause, and replace iron. Oral iron is usually first-line; taking it on alternate days may improve absorption and reduce side effects. Intravenous iron is used when oral iron is not tolerated, is ineffective, or when rapid repletion is needed.
• Anaemia of inflammation: treat the underlying condition; iron supplements may help only if true deficiency coexists.
• Haemochromatosis: regular venesection (removing blood), typically 450–500 mL every one to two weeks until ferritin is reduced, then maintenance. Treating early prevents liver cirrhosis, diabetes, arthritis and heart problems.

Screening for haemochromatosis

Population screening for haemochromatosis is not routinely recommended, but testing is advised for people with suggestive symptoms or findings and for first-degree relatives (parents, siblings and children) of anyone diagnosed with HFE haemochromatosis. Relatives are usually offered a fasting TSAT, ferritin and HFE genetic test. Because iron accumulates over decades, a normal result in a young relative may be repeated in later years. The UK Biobank study found that C282Y homozygosity was more strongly associated with liver disease, arthritis and diabetes than previously thought, especially in men, which has renewed interest in earlier detection.

When to see a doctor

See a clinician if your TSAT is below 20%, particularly with a low ferritin, anaemia, fatigue, breathlessness, heavy periods, or any sign of bleeding from the gut (black stools, blood in stools). Men and post-menopausal women with iron deficiency should be assessed for a gastrointestinal cause.

Also see a clinician if your TSAT is above 45% on a fasting test, especially with raised ferritin, abnormal liver tests, joint pain, unexplained fatigue, diabetes or a family history of haemochromatosis. Do not take iron supplements unless iron deficiency has been confirmed.