Thyroid
What is Free T4?
your main active thyroid hormone
- Unit
- pmol/L
- Sample
- Serum
- Fasting
- No fasting needed
- Turnaround
- 2 days
Free T4 is the free, biologically active form of thyroxine. It complements TSH and is needed for a full picture of thyroid function.
T4 is the main hormone the thyroid produces. Most of it in the blood is protein-bound; only the free fraction is biologically active. When TSH is abnormal, free T4 helps determine whether disease is present and how severe it is.
What does low Free T4 mean?
Low free T4 indicates underactive thyroid.
What does high Free T4 mean?
High free T4 indicates overactive thyroid.
Panels that measure Free T4
- Thyroid Test Base
- Menopause Test
- Performance Test Plus
- Health Check Plus
- Female Hormone Test Plus
- Stress Test Plus
- Thyroid Test Plus
- Thyroid Test Complete
- Performance Test Complete
- Female Hormone Test Complete
- Stress Test Complete
- Health Check Complete
- Health Check Man
- Health Check Kvinna
Reading
More markers in the same area
Launching in Stockholm in 2026.
Want to know when you can order?
This is general information about the marker, not an assessment of your values and not medical advice. Last updated: August 2026.