Total T3 (triiodothyronine)
Also called: Total T3, T3 total, Total triiodothyronine, Triiodothyronine total, Triiodothyronine
All the triiodothyronine in blood. Present in smaller amounts than T4 but stronger, and read beside TSH rather than alone.
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What it measures
Triiodothyronine is the more potent of the two thyroid hormones. Our source puts it plainly: T3 is present in a smaller quantity than T4, yet its potency is greater. Most of it is not made by the thyroid directly — it is converted from T4 in the tissues, which is why a T3 result reflects both the gland and the body's handling of its hormone.
Total T3 counts all of it, bound and free together. As with T4, the bound fraction moves whenever the carrier proteins move, so the total answers "how much is present" rather than "how much is active".
Typical reference ranges
Roughly 80–200 ng/dL in adults, per the Israeli patient reference we cite. That is about 1.2–3.1 nmol/L. Some laboratories print a lower band, nearer 60–180 ng/dL.
The range printed beside your value is the one that counts. Pregnancy and oestrogen-containing medication raise total T3 by raising the carrier proteins, without the gland having changed.
What a high value can mean
- An overactive thyroid, the commonest reason.
- T3 thyrotoxicosis, where T3 is raised while T4 is still within range — the reason this test is ordered when TSH is low but T4 looks normal.
- A benign T3-secreting adenoma of the gland.
- Hashimoto's thyroiditis, which can raise it during an inflammatory phase even though it more often ends in underactivity.
- Medication, which can shift the figure without the gland having changed.
What a low value can mean
- Serious illness of any kind. A low T3 in an unwell person is often the body converting less T4 into T3 rather than a thyroid problem — it tends to recover with the illness.
- Undernutrition.
This is why a low T3 alone is rarely treated as a thyroid diagnosis: the question is usually what else is going on.
Symptoms to look out for
A total T3 inside its range is not felt. Where the thyroid is genuinely overactive, the symptoms belong to that state: a racing heart, weight loss, tremor, heat intolerance, restlessness.
A T3 lowered by illness or by carrier proteins produces no thyroid symptoms at all.
Many out-of-range results cause no symptoms at all - this is context, not a diagnosis.
When to discuss with a doctor
T3 is not normally the first thyroid test, and an isolated result outside the range is read together with TSH and T4 rather than acted on by itself. We'd suggest speaking to your doctor sooner if it comes with a fast or irregular heartbeat, marked weight loss, trembling, heat intolerance or unusual anxiety and sleeplessness — and if you have been seriously unwell recently, say so, because that alone lowers T3.