What we measure
This test measures levels of hormones that control thyroid function and that are produced by the thyroid gland. Together, these readings can tell us whether your thyroid is working properly and making the right amount of hormones. Thyroid hormones control how your body uses energy—affecting your weight, mood, and more. If you have too many, or not enough of them, it can cause health problems.
Free T4 (Thyroxine)
This is the main hormone produced by your thyroid. It regulates how your body uses energy. By measuring the amount of T4 that’s available (“free”) for your body to use, we can find out how well your thyroid is working.

This test can help indicate whether you’ve got a thyroid disorder
Your thyroid is a butterfly-shaped gland located at the front of your neck. It produces essential hormones which control how your body uses energy and affect nearly every organ in the body. Thyroid hormones can influence your weight, hair loss, mood, and more.
If your levels of thyroid hormones are too low (hypothyroidism) or too high (hyperthyroidism), it can be a sign of a thyroid disorder. Getting a blood test is the only way to find out if these hormones are out of balance.
Hypothyroidism affects around 2% of the UK population, with women up to 10 times more likely to be affected. Here, the thyroid doesn’t produce enough hormones, causing symptoms like fatigue, dry skin, weight gain, muscle weakness, and more.
Hyperthyroidism is when the thyroid makes too many hormones. It affects around 2% of women and 0.2% of men in the UK, and can bring on symptoms like weight loss, nervousness, insomnia, fast heart rate, and more.
Your results:
what to expect
Your results will tell you how much TSH and T4 you have inside your body and whether this falls within a healthy range.
The brain produces more TSH when it wants the thyroid to work harder (make more hormones) and makes less to tell it to cool off (make less hormones).
So, high TSH and low T4 suggests that you’ve not got enough thyroid hormones, which is a sign of hypothyroidism.
On the other hand, low TSH and high T4 can mean that you’ve got too many hormones, which may signal hyperthyroidism.
These readings can help to indicate whether you’ve got a thyroid disorder but aren’t a diagnosis in themselves. We’d recommend speaking with a doctor if you’d like to better understand your results.

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Tell the GP what the problem is during your consultation and they’ll take it from there. Prescriptions can be picked up at your local pharmacy.
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FAQs
Thyroid blood tests may give false results if you’re taking biotin, a vitamin B supplement that is sometimes found in multivitamins. To make sure your test is accurate, stop taking biotin at least 48 hours before blood is taken.
Other than that, there’s nothing else specific you need to do to prepare.
The test itself will be over in a matter of minutes. You’ll sit in a chair at your local pharmacy as the healthcare provider draws blood from your arm.
Your results will be available 2 working days after the test.
Blood tests are the most accurate way to identify thyroid problems. Symptoms of thyroid disease can be very general and caused by a number of other conditions, so getting a test can help you figure out whether they’re linked to your thyroid health or something else.
All Tuli tests are validated by HCPC clinical scientists and GMC registered doctors. We’re also regulated by the CQC, which is a quality mark for health services you can trust, and UKAS accredited. You can find us listed on the UK government website.
Yes, absolutely. You can take the test at any time during your menstrual cycle, including whilst on your period.
Hypothyroidism is a deficiency of thyroid hormones, which can cause some body functions to slow down. Symptoms can vary depending on how severe your hormone imbalance is, and tend to develop slowly—often over a number of years.
Signs of hypothyroidism include:
- Fatigue and sluggishness
- Increased sensitivity to cold
- Constipation
- Dry skin
- Weight gain
- Puffy face
- Having a hoarse voice
- Muscle weakness
- Elevated blood cholesterol level
- Muscle aches, tenderness, and stiffness
- Pain, stiffness, or swelling in your joints
- Heavier than normal or irregular menstrual periods
- Thinning hair
- Slowed heart rate
- Depression
- Impaired memory
- Enlarged thyroid gland (goitre)
People with hyperthyroidism have too many thyroid hormones, which can cause many body functions to speed up.
Symptoms include:
- Increased heat tolerance
- Rapid heartbeat
- Nervousness
- Insomnia
- Breathlessness
- Fast heart rate
- Anxiety
- Hand tremors
Certain medications and supplements can alter the results of your thyroid test. If you’re taking any medication, including those for thyroid disorders, it’s important you tell your healthcare provider before you do the test.
Biotin is a vitamin B supplement that can affect your test results. It can be taken on its own and is sometimes included in multivitamins. It’s recommended that you stop taking biotin at least 48 hours before your test.
This depends on your doctor’s advice and whether you have a thyroid disorder.
The British Thyroid Association recommends doing a test once per year if you have been diagnosed with a thyroid disorder, have had previous treatment for an overactive thyroid (hyperthyroidism), or have undergone certain cancer treatments.
Your doctor might recommend getting tested more frequently if you’re undergoing specific thyroid treatment.
If you aren’t sure whether you have a thyroid disorder, the NHS recommends getting a test if you start to experience symptoms that could be related to one. The earlier a thyroid condition is diagnosed, the better.
