Transferrin Saturation (TSAT) Calculator

Calculate transferrin saturation from serum iron and TIBC, and read it against the thresholds for iron deficiency and iron overload.

Last updated 31 Aug 2026

Transferrin Saturation (TSAT)

Iron ÷ TIBC

Serum iron (µg/dL)Sample fasting in the morning.

TIBC (µg/dL)Or use UIBC + iron.

28.8%Example

Serum iron 95 µg/dL, TIBC 330 µg/dL

Formula

TSAT (%) = (Serum iron ÷ TIBC) × 100

Serum iron: µg/dL (or µmol/L — units must match)
TIBC: µg/dL, or serum iron + UIBC
TSAT: percentage of transferrin binding sites occupied by iron

Worked example

Serum iron 95 µg/dL, TIBC 330 µg/dL
(95 ÷ 330) × 100 = 28.8%
Within the normal 20–45% range

Thresholds

Because both numerator and denominator are units of iron, the ratio is the same whether the inputs are in µg/dL or µmol/L.
TSAT	Interpretation	Next step
< 16%	Iron-restricted erythropoiesis	Ferritin and CRP
16 – 20%	Marginal iron supply	Ferritin; treat if < 100 µg/L
20 – 45%	Normal	—
> 45%	Possible iron overload	Fasting repeat, ferritin, HFE genotype

Why saturation beats serum iron

Transferrin saturation is the proportion of transferrin binding sites currently carrying iron, and it is the closest routine measure of how much iron is actually reaching the erythroid marrow. It works because its two components move in opposite directions in iron deficiency: serum iron falls while TIBC rises, so the ratio drops faster and more reliably than either number alone.

That amplification is why saturation, not serum iron, belongs in a diagnostic algorithm. It is also why saturation is the recommended screening test for hereditary haemochromatosis — the earliest biochemical abnormality in HFE disease is a raised saturation, appearing years before ferritin climbs.

The caveats follow from the inputs. Serum iron has a large diurnal swing and rises after supplements, so a saturation calculated on an afternoon sample or a few hours after a tablet can mislead in either direction. Inflammation lowers both iron and TIBC, which compresses the ratio and produces low saturations in anaemia of inflammation without absolute deficiency. Sampling fasting in the morning, off iron for 24 hours, removes most of this noise.

Frequently asked questions

What is a normal transferrin saturation?

Roughly 20% to 45% in adults. Below 20% suggests iron-restricted erythropoiesis; below 16% is the conventional threshold for iron deficiency. Above 45% raises the possibility of iron overload.

Does it matter whether I use µg/dL or µmol/L?

No. Both serum iron and TIBC are expressed in units of iron, so as long as they are in the same units the ratio is identical.

Can transferrin saturation be low without iron deficiency?

Yes. Inflammation lowers serum iron by sequestering iron in macrophages while also lowering transferrin, giving a low saturation with adequate or increased stores. Ferritin and CRP separate the two.

What saturation triggers haemochromatosis testing?

A fasting transferrin saturation persistently above 45% warrants ferritin measurement and, if that is also raised, HFE genotyping.

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References

Camaschella C. Iron deficiency. Blood. 2019;133(1):30–39.
Kowdley KV et al. ACG Clinical Guideline: hereditary hemochromatosis. Am J Gastroenterol. 2019;114(8):1202–18.