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Thyroid Function Blood Test

Thyroid Function Blood Test


The Thyroid Function Blood Test checks your thyroid stimulating hormone (TSH), free T3 (FT3) and free T4 (FT4) to see if you have the right level of thyroid hormones for a healthy metabolism.
Blood sample 3 biomarkers included Results estimated in 2 working days from sample receipt at lab
Thyroid Function Blood Test
Thyroid Function Blood Test
Thyroid Function Blood Test
Thyroid Function Blood Test
Thyroid Function Blood Test

Is it for you?

This test investigates symptoms that could be caused by an overactive or underactive thyroid, like changes in your weight, energy, mood, skin or hair.

If you are being treated for an underactive thyroid, yet still experience symptoms, this test can help explain your systems as it measures three thyroid hormones, including FT3, which your doctor may not routinely check. If you already take thyroid medication, like levothyroxine, you can find out if your dose is working well with this thyroid test.

What's included?

Biomarker profile

  • Thyroid Hormones

Thyroid Hormones (3 Biomarkers)

Special instructions

Please take your sample in the morning. 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.

From the expert

Our Thyroid Function Blood Test is an excellent test to check and monitor your three key thyroid hormone levels – TSH, FT3 and FT4. The thyroid gland produces two of these hormones, T3 and T4, which are bound to proteins as they are transported around the body. When thyroid hormones are bound, they are not readily available to your cells. This test measures the level of free or unbound thyroid hormones, which are biologically active, as they are a better measure of your thyroid function than measuring total levels of T4 and T3 - and they are more likely to explain any symptoms that you may have. 

Many routine tests that only include TSH and FT4 don't identify people who do not convert FT4 to the more biologically active FT3 easily. It is possible to have optimal levels of TSH and FT4 but still experience symptoms of an underactive thyroid if your levels of FT3 are low. This is particularly important if you are being treated for an underactive thyroid yet still experience symptoms. Measuring your FT3 is also important if you are taking some form of T3 medication like liothyronine or natural desiccated thyroid (NDT).

The third hormone, TSH, is produced by the pituitary gland in the brain. When functioning properly, it stimulates the thyroid gland to produce your thyroid hormones (mostly T4). We can think of this as a control hormone as it is responsible for controlling the levels of your thyroid hormones. High levels of TSH can signify that your thyroid is struggling to produce enough T4 for your body's needs. TSH on its own does not necessarily give a true picture of your thyroid function, which is why it is important to test the thyroid hormones too. 

Dr Sam Rodgers MBBS, MRCGP
Chief Medical Officer


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).

Have a look at our Thyroid Health Guide for how your thyroid could hold the answers to better skin, losing weight and regaining your energy.
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?
How often you should take a thyroid test will depend on whether you have been diagnosed with a thyroid disorder and, importantly, whether you are experiencing symptoms.,br.,br.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. Our Thyroid Health Guide explains what frequency of testing may be right for you, depending on your results and symptoms.
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.

Why take this test?

  • Test your TSH, FT4 and FT3.
  • Investigate symptoms of an underactive or overactive thyroid.
  • See if your current thyroid medication dose is working.
  • Take a more in-depth look at your thyroid than is routinely measured.

Laboratories you can trust

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

Dr Sam Rodgers - Chief Medical Officer

Expert advice with your results

Get trusted advice and comments from one of our doctors based on your results.

Your personal 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

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.


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.