thyroid · FT4 · Free T4
Free T4 (Free Thyroxine)
The active, unbound form of the main thyroid hormone. It's interpreted alongside TSH: a low free T4 with high TSH suggests an underactive thyroid, while a high free T4 with low TSH suggests an overactive one.
This page is general wellness education, not medical advice. Your own lab’s reference range and your clinician’s interpretation always take precedence.
Typical reference range
| Group | General range |
|---|---|
| Adults | ~0.8–1.8 ng/dL (assay-dependent) |
Units: ng/dL. Ranges vary by lab and assay — read yours against the range printed on your own report.
What high Free T4 (Free Thyroxine) can mean
- Hyperthyroidism
- Graves' disease
- Excess thyroid medication
- Thyroiditis (early)
What low Free T4 (Free Thyroxine) can mean
- Hypothyroidism
- Hashimoto's thyroiditis
- Pituitary problems