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Total Thyroxine (T4) Blood Test
Total Thyroxine (T4) Blood Test
Total Thyroxine (T4) Blood Test
Total Thyroxine (T4) Blood Test

Total Thyroxine (T4) Blood Test

Thyroxine (T4) is the main hormone produced by the thyroid gland. This blood test measures levels of T4 to help in the diagnosis of thyroid disease.
Blood sample 1 biomarker included 2 working days turnaround
from sample receipt at lab

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.
To produce thyroxine, the thyroid gland needs iodine from the food we eat. Thyroxine is called T4 because it contains 4 atoms of iodine. Although it is the most plentiful of the thyroid hormones, it is not biologically active and does not govern metabolism in our cells. That job is undertaken by triiodothyronine, or T3. T4 converts to T3 by the removal of an atom of iodine.

Thyroxine is typically measured in thyroid function tests because a low T4 reading is likely to indicate insufficient levels of T3 (and therefore a slow metabolism) while high levels of T4 tend to lead to excess T3 (resulting in an overactive metabolism).

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.