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Transferrin saturation (TSAT) calculator for iron deficiency and overload

Calculate transferrin saturation from serum iron and total iron-binding capacity, and read it with ferritin to look for iron deficiency or iron overload.

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µg/dL

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µg/dL

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ng/mL

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Results

Transferrin saturation

15.0%

Below 16%: iron-restricted red cell production, as in iron deficiency
Ferritin
20 ng/mL
Below 30: iron stores are low
Total iron-binding capacity
400.0 µg/dL
Unsaturated iron-binding capacity
340.0 µg/dL

What transferrin saturation measures

Iron travels in the blood bound to a protein, transferrin. Transferrin saturation (TSAT) is the percentage of transferrin’s iron-binding sites that are occupied. It shows how much iron is available for making red blood cells right now, while ferritin reflects how much is stored.

The formula

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

In the United States, both values are usually reported in µg/dL. The calculator also shows the unsaturated iron-binding capacity (UIBC), TIBC minus serum iron.

Worked example

Serum iron 60 µg/dL, TIBC 400 µg/dL, ferritin 20 ng/mL:

Result Value
Transferrin saturation 15%, below 16%
Ferritin 20 ng/mL, low stores
UIBC 340 µg/dL

A low saturation, a high TIBC and a low ferritin together are the classic pattern of iron deficiency.

Reading the result

TSAT Usual meaning
Below 16% to 20% Not enough iron reaching the marrow: iron deficiency, or iron held back by inflammation
About 20% to 45% Usual range
Above 45% Possible iron overload, such as hereditary hemochromatosis

Ferritin makes the difference

  • Low TSAT, low ferritin (below about 30 ng/mL): iron deficiency.
  • Low TSAT, normal or high ferritin: often the anemia of inflammation, where iron is present but locked away. Ferritin rises with inflammation, infection, liver disease and cancer.
  • High TSAT, high ferritin: iron overload is possible. Hereditary hemochromatosis is usually confirmed with genetic testing for the HFE gene.

Practical points

  • Serum iron rises after meals and iron supplements and is higher in the morning, so labs often prefer a fasting morning sample, and an abnormal TSAT is usually repeated.
  • Oral contraceptives and pregnancy raise TIBC and can lower the saturation.
  • Some labs measure transferrin instead of TIBC; TIBC in µg/dL is roughly transferrin in mg/dL × 1.4.
  • Reference ranges differ between labs and between men and women.

This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.

Frequently asked questions

How is transferrin saturation calculated?

TSAT = serum iron ÷ total iron-binding capacity × 100. With iron at 60 µg/dL and TIBC at 400 µg/dL, TSAT is 15%.

What is a normal transferrin saturation?

Usually about 20% to 45%, with some variation between laboratories. Below 16% to 20% points to iron-restricted red cell production; above 45% raises the question of iron overload.

Why check ferritin too?

Ferritin reflects iron stores. A ferritin below 30 ng/mL with a low TSAT strongly suggests iron deficiency. Inflammation raises ferritin, so a normal value does not rule out deficiency in that setting.

Should I fast before an iron test?

Serum iron rises after meals and is highest in the morning, so many labs ask for a fasting morning sample. A high TSAT is usually repeated before testing for hemochromatosis.

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Results are estimates provided for information purposes. They do not replace professional advice.

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