thyroid · FT3 · Free T3
Free T3 (Free Triiodothyronine)
The active, unbound form of the more potent thyroid hormone. It's used with TSH and free T4 to fine-tune the thyroid picture, and can fall during illness even when the thyroid itself is fine.
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 | ~2.3–4.2 pg/mL (assay-dependent) |
Units: pg/mL. Ranges vary by lab and assay — read yours against the range printed on your own report.
What high Free T3 (Free Triiodothyronine) can mean
- Hyperthyroidism
- Graves' disease
- Excess thyroid medication
What low Free T3 (Free Triiodothyronine) can mean
- Hypothyroidism
- Acute/severe illness (non-thyroidal)
- Fasting