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Free Thyroxine (FT4) Blood Test
Free Thyroxine (FT4) Blood Test
Free Thyroxine (FT4) Blood Test
Free Thyroxine (FT4) Blood Test

Free Thyroxine (FT4) Blood Test

T4 (thyroxine) is the main hormone produced by the thyroid gland. This simple finger-prick blood test measures levels of unbound or free T4.

Is it for you?

Do you have symptoms which you think might be due to an overactive or underactive thyroid? Have you already had a test for TSH (thyroid stimulating hormone) which was borderline and left you wondering about your levels of free T4? If you want a simple finger-prick test which measures the amount of available T4 in your blood, then this is the right test for you.
Blood sample 1 biomarker included 2 working days turnaround

What's included?

Biomarker profile

  • Thyroid Hormones

Thyroid Hormones (1 Biomarker)

Special instructions

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. Some conditions can cause the number of carrier proteins in the blood to rise or fall. Raised oestrogen due to pregnancy or birth control pills, elevated cortisol and liver failure can all affect the level of carrier proteins. The more T4 that is attached to carrier proteins, the less there is available to be converted to T3, which regulates metabolism. This is why looking at levels of free T4 can be helpful in diagnosing a thyroid condition when total T4 levels are within the normal range.

Dr Sam Rodgers MBBS, MRCGP

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.