Free T3 (free triiodothyronine) blood test
Quick answer: A free T3 test measures the active, unbound form of triiodothyronine, one of the thyroid hormones. Doctors order it with TSH and free T4 to look into an overactive thyroid or to follow thyroid treatment.
- SampleBlood
- TakesAbout 5 minutes
- Before the testNo special preparation is usually needed.
- In fertility careThyroid problems can affect ovulation and pregnancy, so thyroid levels are commonly checked before fertility treatment and in pregnancy.
How the test is done
- 1You can usually come at any time of day
- 2A needle draws blood from a vein
- 3The lab measures free T3
- 4It is usually read with TSH and free T4
What your results can mean
Reading your report
Ranges differ between labs and in pregnancy, so discuss your result with your doctor.
If the result is outside the usual range
A high level can be seen with an overactive thyroid, such as Graves' disease or thyroid nodules. A low level can be seen with an underactive thyroid or during serious illness.
Who usually has this test
People with symptoms of an overactive thyroid, such as weight loss, fast heartbeat and anxiety, and people on thyroid treatment.
Risks and aftercare
Most people have no after-effects beyond a little bruising.
Names and options
Also called: FT3, free T3
Listed by the hospital as
- FREE T3 (TRIIODOTHYRONINE), SERUM
Questions about this test
Why is free T3 tested if free T4 is normal?
In some overactive thyroid conditions, only T3 is raised. Checking free T3 helps find this.
Can illness affect free T3?
Yes. During serious illness or fasting, the body makes less T3. This often settles without thyroid treatment.
Does biotin affect thyroid tests?
High-dose biotin supplements can interfere with some thyroid tests. Tell your doctor if you take biotin or hair and nail supplements.
Related tests
Tamara Hospital & IVF Centre, Rajajinagar
34/3, 10th Cross Road, opp. Vardhaka Sardar Patel School, 1st N Block, 2nd Stage, Rajajinagar, Bengaluru 560010
The hospital is open 24 hours. Call before you come to check the timing for your scan or sample collection.
Get directions ↗IVF Pulse fertility care at Tamara Hospital →
Reception
Waiting area
IVF lab
This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.