How reports print it
FT4Свободный Т4Т4 свСв Т4Тироксин свободныйСвободный тироксинFree thyroxineT4 free
What it shows
Free thyroxine — the main thyroid hormone in its active form, not bound to protein.
Units and conversion
Base unit: pmol/L.
- 1 ng/dL = 12.87 pmol/L · 1 pmol/L = 0.0777 ng/dL
Typical ranges
Your laboratory’s range comes first — it is printed on the report next to the result. Below is one laboratory’s adult range with its method: a reference, not a rule.
| Who | Range, pmol/L |
|---|---|
| Adults, 18–20 years | 12.6–21 |
| Adults, 21 years and older | 10.8–22 |
Range source: Лаборатория Хеликс — Тироксин свободный (Т4 свободный)
Good to know
Ranges depend on the platform: 10.8–22.0 pmol/L at Helix, 9.0–19.05 at Invitro. Conversion: ng/dL × 12.87 = pmol/L.
Why it can be higher
Common reasons discussed with a doctor. This is not a diagnosis.
- An overactive thyroid
- Taking thyroid hormones shortly before the test
Why it can be lower
- An underactive thyroid
- Acute and chronic illness outside the thyroid
- Some medicines
What to ask a doctor
- How does free T4 fit with TSH?
- Should the test be taken before the morning tablet?
Whom to see
A GP or internist; then an endocrinologist.