Free Triiodothyronine (Free T3)
The most biologically active thyroid hormone. Helps evaluate hyperthyroidism and thyroid conversion disorders.
Typical normal range
2.3–4.2 pg/mL
If high ↑
T3 toxicosis, hyperthyroidism
If low ↓
Hypothyroidism, low T4-to-T3 conversion (selenium deficiency)
What is a normal Free Triiodothyronine level?
A typical reference range is 2.3–4.2 pg/mL. Ranges vary between laboratories and can depend on age and sex, so compare your result with the range printed on your own report.
What does a high Free Triiodothyronine level mean?
T3 toxicosis, hyperthyroidism. A single result rarely gives a diagnosis on its own; your doctor will interpret it alongside your symptoms and other tests.
What does a low Free Triiodothyronine level mean?
Hypothyroidism, low T4-to-T3 conversion (selenium deficiency). Your doctor will interpret it alongside your symptoms and other tests.
About the Thyroid Panel
Thyroid tests show how well your thyroid gland is working. The thyroid helps control metabolism, so an over- or under-active thyroid can affect energy, weight, mood and heart rate.
See your own Free Triiodothyronine result explained
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Medical disclaimer: Reference ranges vary by laboratory, age, sex, and clinical context. This page is for educational purposes only and is not a diagnosis. Always discuss your results with a qualified healthcare professional.