β All markers
Thyroid Β· pmol/L
Free T4 (Thyroxine)
The main thyroid hormone β measures the active circulating pool.
What it is
Free T4 is the unbound (biologically active) form of thyroxine produced by the thyroid gland. It is the precursor to the more potent T3 and reflects thyroid gland output directly.
Why it matters
Free T4 is ordered alongside TSH to confirm thyroid dysfunction. A high TSH with low Free T4 confirms primary hypothyroidism. Normal TSH with low Free T4 may indicate central (pituitary) hypothyroidism. Free T4 is the standard monitoring marker during levothyroxine replacement therapy.
How to test
Blood test. Typically ordered alongside TSH.
This information is for educational purposes only. Always discuss testing and interpretation of results with your care team.
Optimal range
Below 12 pmol/L
low β hypothyroid
12β22 pmol/L
normal
Above 22 pmol/L
elevated β hyperthyroid
How often
When TSH is abnormal, or every 6β12 months if on thyroid replacement.
Tags
thyroid
hormones
metabolism