β All markers
Thyroid Β· pmol/L
Free T3 (Triiodothyronine)
The active thyroid hormone β the metabolically potent form.
What it is
Free T3 is the biologically active form of thyroid hormone, primarily converted from T4 in peripheral tissues (especially the liver). It is responsible for most of the metabolic effects of thyroid hormones.
Why it matters
Some people have normal TSH and T4 but impaired conversion of T4 to T3 β leaving them with functional hypothyroid symptoms. This occurs with chronic illness, stress, nutritional deficiencies, and sometimes after cancer treatment. Checking Free T3 alongside T4 reveals this "low T3 syndrome." It is also useful for monitoring people on desiccated thyroid or T3 supplementation.
How to test
Blood test. Ordered alongside TSH and Free T4 for full thyroid picture.
This information is for educational purposes only. Always discuss testing and interpretation of results with your care team.
Optimal range
Below 3.5 pmol/L
low β possible impaired T4βT3 conversion
3.5β6.5 pmol/L
normal
How often
When thyroid symptoms persist despite normal TSH/T4, or every 12 months as part of comprehensive panel.
Tags
thyroid
hormones
metabolism
fatigue