Transferrin saturation Transferrin Saturation (TSAT)
How full your iron carriers are, given as a percentage.
Also printed asTSAT · Iron Saturation · %Sat · TS%
What it measures
The share of your iron transport that is actually carrying iron.
The most reliable single read on iron supply: below 20% supports deficiency, above 45% is the threshold that prompts an overload check.
Why it matters for how long you stay well
It catches iron running short before haemoglobin falls, and a persistently high percentage is the screening signal for iron building up too much, which damages liver, heart and joints over decades.
How it shows up in daily life
A low percentage often explains tiredness and breathlessness even when haemoglobin still looks acceptable.
High and low readings
When it reads high
Iron transport is full; haemochromatosis is worth ruling out above 45%.
When it reads low
Iron transport is running near empty, which supports a deficiency even when ferritin looks normal.
What moves it
Daily life
- iron in your diet
- inflammation, which distorts it in both directions
- heavy periods
- blood donation
Medicines known to shift it
- iron supplements (raise it)
Listed so a result can be read in context. It is not advice to start, stop or change any medicine; that decision belongs with your physician.
Read it with
Markers that move this one, or that this one moves. One number read alone can mislead.
- Ferritin, your iron storeKnown mechanism
Ferritin moves with it
Saturation is how full those carriers are. Empty stores mean less iron to load onto them, so saturation falls alongside the stores.
- Circulating ironKnown mechanism
Circulating iron is part of its calculation
Saturation is your circulating iron divided by your binding capacity. It is arithmetic on two results you already have, not another test on your blood.
- Iron-binding capacityKnown mechanism
Iron-binding capacity pulls it down
Binding capacity is the bottom of that fraction. More carriers means the same iron fills a smaller share of them, so the percentage falls.
Common questions
What does Transferrin Saturation (TSAT) measure?
The share of your iron transport that is actually carrying iron. The most reliable single read on iron supply: below 20% supports deficiency, above 45% is the threshold that prompts an overload check.
What does a high Transferrin saturation result usually mean?
Iron transport is full; haemochromatosis is worth ruling out above 45%.
What does a low Transferrin saturation result usually mean?
Iron transport is running near empty, which supports a deficiency even when ferritin looks normal.
What is the usual reference range for Transferrin saturation?
A broad adult reference band is 20–50 %. Labs differ, so read your result against the band printed on your own report.
Educational only, not a diagnosis. A single number means little without your history and the rest of your panel, so discuss your own results with your physician.
Typical adult reference band
- Adults
- 20–50 %
Labs differ. The band printed on your own report is the one that applies to your result.
Reported in %
Ageing relevance
3/5
A moderate ageing association; used in clinical longevity panels.
Worth knowing
It is serum iron divided by binding capacity, so it is arithmetic on two results you already have.
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