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Free Triiodothyronine (FT3) Blood Test
Free Triiodothyronine (FT3) Blood Test
Free Triiodothyronine (FT3) Blood Test
Free Triiodothyronine (FT3) Blood Test

Free Triiodothyronine (FT3) Blood Test

Triiodothyronine (T3) is one of two thyroid hormones produced by the thyroid gland. This test measures the available form of T3, known as free T3.

Is it for you?

Do you have symptoms of an overactive or underactive thyroid? Are you having a test for TSH (thyroid stimulating hormone) and FT4 (free thyroxine) and want to test your FT3 for completeness? Are you being treated for an underactive thyroid with liothyronine (T3) and want to monitor your T3 levels? If you want to check your T3 status to complement other thyroid function tests you may be having, this test is right for you.
Blood sample 1 biomarker included 2 working days turnaround

What's included?

Biomarker profile

  • Thyroid Hormones

Thyroid Hormones (1 Biomarker)

Special instructions

If you are taking a T3 containing medication take your test in the hour prior to your dose of medication. Do not take biotin supplements for 2 days prior to this test. If you are taking prescribed biotin you should discuss this with your doctor.
The vast majority of thyroid hormones circulating in the blood are bound to carrier proteins. This test measures the level of the active thyroid hormone T3 which is free (not bound to protein) and therefore available to your cells to regulate metabolism. Raised levels of FT3 indicate an overactive thyroid whereas low levels indicate that your thyroid is not producing enough thyroid hormones.

Other factors may influence your FT3 levels, such as your ability to convert T4 (thyroxine) to T3. 

A Free T3 test is of limited value when looked at in isolation. We therefore recommend that Free T3 is tested alongside FT4 (free thyroxine) and TSH (thyroid stimulating hormone). 

Dr Sam Rodgers MBBS, MRCGP

Why take this test?

  • You have symptoms of an abnormal thyroid function
  • You wish to check an already diagnosed thyroid condition
  • You are having a test which includes TSH and FT4 and you wish to check your FT3 for a comprehensive view of your thyroid hormones
  • You take T3 as part of your thyroid replacement and want to check your levels

How it works

  • Take the test

    Collect your sample at home, visit a partner clinic, or we can even send a nurse to you.
  • Post your sample

    Send your sample back on the same day you take it in the freepost pack to our laboratory.
  • Get your results

    View your results with doctor's advice on your personal dashboard.
Laboratories you can trust

Laboratories you can trust

Trusted by the NHS and private clinics alike, you can be sure of the highest testing standards from our fully accredited partner laboratories.

Expert interpretation <br>
of your results

Expert interpretation
of your results

One of our team of doctors will review your results and give you personalised advice based on your medical history, lifestyle and health and fitness goals.

Your personal<br>
health centre

Your personal
health centre

Discover the easy way to track your health through our online portal, View your results with doctor's advice, monitor any changes over time and see the improvements you can make to your health with simple lifestyle changes.

Questions? Let us help

Questions? Let us help

Our customer care team is on-hand to help you find the test that's right for you. Get in touch via phone, live chat or email.

What our customers say

We ask every Medichecks customer about their experience - read what they have to say


Our tests are not a substitute for seeing your doctor, especially if you are suffering symptoms. Our doctors will interpret your results based on the information you have provided, but will not diagnose, consult or provide any treatment. You will be advised to see your doctor for any necessary follow-up action.