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The Thyroid Hormone Blood Test is also commonly referred to as a Thyroid Function Test. This is a simple blood test that checks the level of thyroid hormones in your blood, including the Thyroid Stimulating Hormone (TSH), Triiodothyronine (T3) and Thyroxine (T4). The results can be compared to the average thyroid activity levels of others your age to determine whether you may have conditions, such as overractive thryoid. Identifying thyroid issues can help your doctor to direct you on the best course of treatment for your individual needs.


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Thyroid Hormones: Your thyroid is a gland in the front of your neck which produces hormones which help to govern your metabolism. It is possible for your thyroid to under-produce or over-produce thyroid hormones. Underactive thyroid leads to symptoms of lethargy, weight gain, dry skin and hair while an overactive thyroid leads to symptoms of feeling nervous and anxious, as well as weight loss. Once diagnosed, thyroid conditions can be treated but even then, it is important to continue to monitor levels of thyroid hormones to ensure that your levels remain optimal.

Free Thyroxine
Thyroxine (T4) is one of two hormones produced by the thyroid gland. It works to speed up the rate of your metabolism. Most T4 is bound to carrier proteins in the blood, but it is only the free, or unbound T4 that is active in the body, which is measured in this test.
Free T3
Triiodothyronine (T3) is the more active of the two thyroid hormones produced by the thyroid gland. Most T3 is bound to protein in the blood. Free T3 measures the level of T3 that is free, or unbound to protein, and is available to regulate metabolism.
The thyroid is a gland at the base of your neck responsible for a number of metabolic processes, including energy expenditure, cardiac function, muscle physiology and substrate turnover. Disturbances in your thyroid function can lead to excess hormone levels (overactive) or diminished levels (underactive), both of which can lead to a decrease in athletic performance. Thyroid Stimulating Hormone (TSH) is produced by the pituitary gland and stimulates the thyroid gland to produce the two thyroid hormones thyroxine (T4) and triiodothyronine (T3). Thyroid hormone production is part of a neuroendocrine cascade. It starts in the hypothalamus with the release of thyrotropin releasing hormone (TRH), which triggers the pituitary gland to produce thyroid stimulating hormone (TSH). This binds to cells in the thyroid gland to release the hormones T3 and T4 (thyroxine). T4 is also converted into T3 (the more active thyroid hormone) at peripheral tissues. It is these hormones which essentially control the metabolism around your body. All these levels are normally held in tight balance through negative feedback loops. Abnormal thyroid function can manifest by over-secretion or under-secreting the thyroid hormones.


Frequently Asked Questions


What is the thyroid?
The thyroid is a butterfly shaped gland that sits under your Adam’s apple. It produces thyroid hormones which help to regulate your metabolism. Sometimes, the thyroid produces too many hormones, leading to an overactive thyroid (hyperthyroidism), or too few, leading to an underactive thyroid (hypothyroid).
What is thyroid disease and who is at risk?
As many as 1 in 20 people are thought to have a thyroid disorder. There are a number of different conditions that can affect the normal functioning of the thyroid, including an underactive thyroid (hypothyroid), an overactive thyroid (hyperthyroidism), autoimmune disease, thyroid swelling (or a goitre), nodules or thyroid cancer. Although anyone can develop a thyroid disorder, factors including being female or over the age of 50, and people with a family history of thyroid problems, can increase an individual’s risk of developing thyroid disease.
How often should I get a thyroid test?
Test will depend on whether you have been diagnosed with a thyroid disorder and, importantly, whether you are experiencing symptoms. You may want to take a thyroid test if you are experiencing symptoms of an overactive or underactive thyroid or if you are managing a thyroid condition.
Can I test my thyroid during pregnancy?
You can test your thyroid during pregnancy as it’s important to have a well-controlled thyroid for the healthy development of the baby. If you have a thyroid condition and are planning to conceive, or when find out you’re pregnant, let your GP know so they can monitor you or take your thyroid test results to your doctor.

Thyroid results during pregnancy:

  • Underactive thyroid during pregnancy – TSH level should be less than 2.5 mU/l in the first trimester and less than 3.0 mU/l in the second and third trimesters.
  • Overactive thyroid during pregnancy – doses may be adjusted through regular monitoring.


Special Instructions

Prepare for your Thyroid Function Blood Test by following these instructions. Please take your sample before 10am. You should take this test before you take any medication or vitamin/mineral supplements. Do not take biotin supplements for 2 days before this test, discuss this with your doctor if it is prescribed.





How it works


  • Place an order and get your test delivered to your door (delivery is free)
  • Take your sample by following the instructions included with the test
  • Send your samples (freepost) back to our UK-based, accredited laboratory
  • Once your results are received, they will be processed in our laboratory
  • One of our doctors will then view your results and prepare a report
  • You will receive your report through our online portal in your account


Post your blood sample on the same day as testing to prevent your blood from being heamolysed which will result in re-testing.



Take your test

Receive & take your chosen blood or healthcare test in the comfort of your own home.


Post your sample

Send your sample back to us in the freepost pack to our UK based laboratory.


Get your results

View your results with our Doctor’s advice on your personal online dashboard.




Our tests are not a substitute for seeing your doctor, especially if you are suffering symptoms. Our healthcare professionals 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.



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