Free Thyroxine (Free T4)
Free T4 is the unbound, active form of thyroxine — the main thyroid hormone. Used to confirm and characterise abnormal TSH results. Low free T4 with high TSH confirms overt hypothyroidism; the opposite confirms hyperthyroidism.
- Category
- Thyroid
- Units
- pmol/L
- Reference range
- 9-19 pmol/L
What does a high Free Thyroxine result mean?
Overt hyperthyroidism, thyroiditis, excess thyroid hormone replacement.
What does a low Free Thyroxine result mean?
Overt hypothyroidism, severe non-thyroidal illness, pituitary dysfunction.
Why does Free Thyroxine matter?
Confirms what TSH suggests. Doesn't replace TSH as the first-line screen.
Want Free Thyroxine interpreted in the context of your full panel? Every FORM bloodwork tier covers it, with an MD walking you through the result.
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