Free Thyroxine (Free T4)
The active, unbound form of the main thyroid hormone. Confirms thyroid dysfunction when TSH is abnormal.
Typical normal range
0.8–1.8 ng/dL
If high ↑
Hyperthyroidism, thyroiditis, excess thyroid medication
If low ↓
Primary or secondary hypothyroidism
What is a normal Free Thyroxine level?
A typical reference range is 0.8–1.8 ng/dL. 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 Thyroxine level mean?
Hyperthyroidism, thyroiditis, excess thyroid medication. 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 Thyroxine level mean?
Primary or secondary hypothyroidism. 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 Thyroxine 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.