Transferrin Saturation (TSAT) Calculator
Calculator
Transferrin Saturation (TSAT) Calculator
Calculate transferrin saturation from serum iron and TIBC, or from transferrin, with UIBC and comparison against the reference range
The calculator applies the formula TSAT = serum iron / TIBC × 100. If you enter transferrin instead of TIBC, TIBC is estimated from the stoichiometric ratio TIBC (µmol/L) = 25.1 × transferrin (g/L): laboratories use slightly different conversion factors, so when the report gives a measured TIBC it is better to use that. The 20–50% reference range and the 45% suspicion threshold are those of the MSD Manuals and the EASL guidelines on hemochromatosis. This is an informational tool: ranges vary by laboratory, sex and age, the result is not a diagnosis and does not replace the laboratory report or a doctor's assessment.
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How the transferrin saturation calculator works
Transferrin saturation, abbreviated as TSAT, tells you how much of the blood's iron-transport capacity is actually occupied by iron. Transferrin is the protein that carries iron around the body: if it carries little, saturation is low, consistent with a deficiency; if it carries a lot, saturation is high and may indicate iron accumulation. It is one of the values of the iron panel and is the parameter that guidelines use as the first filter when iron overload is suspected.
You can work in µg/dL, the most common unit in Italy, or in µmol/L: the result is the same, because saturation is a ratio between homogeneous quantities. Everything happens in your browser: the values you type are not sent to any server.
The formula and the data you need
The calculation is a division:
| Quantity | Formula | What it is |
|---|---|---|
| Transferrin saturation (TSAT) | serum iron / TIBC × 100 | percentage of transport capacity already occupied by iron |
| UIBC | TIBC − serum iron | iron-binding capacity still free |
Serum iron is the iron that circulates bound to transferrin. TIBC (total iron-binding capacity) is the maximum amount of iron the blood could bind. Many reports show both and the calculator uses the two numbers directly. If instead you find transferrin in mg/dL or g/L in place of TIBC, TIBC is derived from transferrin — and this is where a caveat is needed.
When TIBC is estimated from transferrin
Each transferrin molecule binds two iron atoms: hence the stoichiometric ratio published in Clinical Chemistry, TIBC (µmol/L) = 25.1 × transferrin (g/L), which in conventional units becomes TIBC (µg/dL) = 1.4017 × transferrin (mg/dL). The calculator uses this factor and states it every time it applies it.
However, it is an estimate, not a measurement. Laboratories that derive TIBC from transferrin do not all use the same factor: a survey of 21 certified laboratories found implicit factors between 0.74 and 1.44, and Mayo Clinic Laboratories declares an empirical one of 1.18. The estimated TIBC may therefore differ from the measured one, and so may the final percentage. If the report shows TIBC, use it; if it only shows transferrin, read the result as an order of magnitude.
Calculation example
First case, with measured TIBC: serum iron 80 µg/dL and TIBC 320 µg/dL.
| Item | Calculation | Result |
|---|---|---|
| Serum iron | from the report | 80 µg/dL (14.33 µmol/L) |
| TIBC | from the report | 320 µg/dL (57.30 µmol/L) |
| UIBC | 320 − 80 | 240 µg/dL (42.98 µmol/L) |
| Transferrin saturation | 80 / 320 × 100 | 25% |
Second case, with transferrin instead of TIBC: serum iron 95 µg/dL and transferrin 250 mg/dL.
| Item | Calculation | Result |
|---|---|---|
| Transferrin | from the report | 250 mg/dL (2.50 g/L) |
| Estimated TIBC | 250 × 1.4017 | 350.4 µg/dL (62.75 µmol/L) |
| UIBC | 350.4 − 95 | 255.4 µg/dL (45.74 µmol/L) |
| Transferrin saturation | 95 / 350.4 × 100 | 27.1% |
For the same case, the alternative formula published in the nephrology literature — TSAT = serum iron / transferrin × 70.9 — gives 26.9%: a difference of two tenths of a point, which is the measure of the uncertainty introduced by the estimate.
How to read the result
| Saturation | How the calculator classifies it |
|---|---|
| below 20% | below the reference range; it is also the iron deficiency threshold in the ESC heart failure guidelines |
| 20–45% | within the reference range and below the suspicion threshold |
| above 45% | above the threshold beyond which the EASL hemochromatosis guidelines call for repeating the test while fasting |
| 50% or more | above the reference range and above the suspicion threshold |
The 20–50% range is the one in the MSD Manuals, professional edition. The 45% threshold comes from the European guidelines on hemochromatosis: the same MSD Manuals state that a saturation below 45% has a negative predictive value of 97% for iron overload, meaning it is very good at ruling it out. Be aware, however: reference ranges change from laboratory to laboratory and vary with sex and age. What counts is the number printed next to your result on the report, not a generic table.
When this calculation is not enough
Transferrin saturation alone does not settle any question. It must be read together with ferritin, the complete blood count and the clinical history: guidelines define suspected hemochromatosis by combining saturation and ferritin, with different thresholds for men and women. Serum iron fluctuates a lot over the course of the day and is affected by meals, so when a value is high the first step is to repeat the blood draw while fasting. Inflammation, liver disease, pregnancy and treatment with iron or estrogen-progestin therapy shift both transferrin and serum iron.
This is an informational tool: it is not a diagnosis and does not replace the laboratory report or the assessment of a doctor, the only one able to read the values in the context of your clinical history. No number calculated on a web page is a reason to start, change or stop a treatment, iron supplements included.
Frequently asked questions
How is transferrin saturation calculated?
Divide serum iron by total iron-binding capacity (TIBC) and multiply by one hundred: TSAT = serum iron / TIBC × 100. The two quantities must be expressed in the same unit, because the result is a ratio. With serum iron of 80 µg/dL and TIBC of 320 µg/dL, saturation is 25%.
How is TIBC derived from transferrin?
With the stoichiometric ratio TIBC (µmol/L) = 25.1 × transferrin (g/L), equal to TIBC (µg/dL) = 1.4017 × transferrin (mg/dL), because each transferrin molecule binds two iron atoms. It is an estimate: laboratories use conversion factors that can differ considerably, so when the report gives a measured TIBC it is better to use that.
What are normal transferrin saturation values?
The MSD Manuals indicate a reference range of 20–50%. However, ranges vary by laboratory, sex and age, so the comparison should be made with the values printed on your report. Below 20% the picture is consistent with iron deficiency; above 45% guidelines call for further investigation.
Does high transferrin saturation mean hemochromatosis?
No. 45% is a suspicion threshold, not a diagnosis: the EASL guidelines first call for repeating the test while fasting and, if the value is confirmed, evaluating it together with ferritin and possibly genetic testing. High saturation can also result from a recent meal, iron supplements, liver disease or other conditions. The decision rests with the doctor.
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