Free Tri-iodothyronine (FT3)
Thyroid blood
What It Is
FT3 is the active form of thyroid hormone, converted from T4 in the body's tissues.
Why It Matters
FT3 is the most metabolically active thyroid hormone and is particularly useful in diagnosing hyperthyroidism.
If Levels Are High
Elevated FT3 may indicate hyperthyroidism, particularly T3 thyrotoxicosis.
If Levels Are Low
Low FT3 may be seen in hypothyroidism or non-thyroidal illness.
Preparation
No special preparation required.
How Often to Test
As clinically indicated, typically alongside TSH and FT4.
Important Disclaimer
This information is for educational purposes only and does not constitute medical advice or diagnosis. Results should be interpreted in clinical context by a qualified healthcare professional. If you have severe symptoms or urgent concerns, seek urgent medical help.