How to know when to get a thyroid test

It’s worth getting tested if you have symptoms of an underactive or overactive thyroid, or a higher risk, for example because of a family history or another autoimmune condition such as type 1 diabetes. Symptoms are often mild, come on slowly and can be caused by other things, so a blood test is the only way to know.

UK screening experts don’t recommend routine thyroid tests for adults who feel well, partly because there’s no evidence that treating early, mild changes helps. If you already have a thyroid condition, or take a medicine that can affect your thyroid, your doctor may suggest regular tests.

An underactive thyroid (hypothyroidism) means your thyroid doesn’t make enough hormone. The NHS lists these symptoms:

• Feeling extremely tired.
• Feeling cold more than usual.
• Putting on weight.
• Constipation.
• Difficulty concentrating or thinking clearly.
• Low mood or depression.
• Dry skin, dry hair or hair loss.
• A croaky voice.
• Irregular or heavy periods.

It can also lower your sex drive. In the UK, the most common cause is Hashimoto’s disease, where the immune system attacks the thyroid.

An overactive thyroid (hyperthyroidism) means your thyroid makes too much hormone. Symptoms can include:

• Nervousness, anxiety and irritability.
• Mood swings and difficulty sleeping.
• Feeling tired all the time.
• Sensitivity to heat, warm skin and sweating.
• A fast or irregular heartbeat.
• Twitching or trembling.
• Weight loss, often despite a bigger appetite.
• Needing to pee more often, diarrhoea and persistent thirst.
• A swelling in your neck (goitre).
• Loss of interest in sex.

About 4 in 5 people with an overactive thyroid have Graves’ disease, an autoimmune condition that often runs in families.

You’re more likely to have a thyroid problem if you:

• Are a woman. Thyroid problems are much more common in women, and an overactive thyroid is about 10 times more common in women than men.
• Have a family history of thyroid problems.
• Have type 1 diabetes, Addison’s disease or another autoimmune condition.
• Have recently had a baby.
• Have had surgery or radiotherapy on your neck, or treatment for an overactive thyroid.
• Take medicines such as lithium or amiodarone.

An overactive thyroid usually starts between the ages of 20 and 40, and smoking raises your risk of Graves’ disease.

Thyroid problems can affect your periods, fertility and sex drive:

• Both an underactive and an overactive thyroid can stop you ovulating.
• An underactive thyroid can cause heavier or irregular periods and a lower sex drive.
• An overactive thyroid can cause lighter, irregular periods and a loss of interest in sex. In men, it can lower sperm count, which usually returns to normal after treatment.

In pregnancy, a thyroid condition that isn’t well controlled can raise the risk of complications such as pre-eclampsia, miscarriage and premature birth, so tell your doctor or midwife if you have one. Around 5 to 10% of women develop inflammation of the thyroid (postpartum thyroiditis) after having a baby, usually within the first year. It often makes the thyroid overactive at first, and it may then become underactive. Read more in “Can STIs affect your period?”

A thyroid test is a blood test that can measure:

• TSH (thyroid stimulating hormone): the hormone your pituitary gland makes to control how much hormone your thyroid produces. It’s usually the first test.
• Free T4 (FT4) and free T3 (FT3): the main thyroid hormones. FT3 is mainly used to check for an overactive thyroid.
• Thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb): these can show whether an autoimmune condition, such as Hashimoto’s disease, is the cause.

Thyroid antibodies aren’t a diagnosis on their own. TPO antibodies are also found in about 1 in 10 people who don’t have a thyroid problem.

Your results are compared with a normal range:

• High TSH and low FT4 suggest an underactive thyroid.
• Low TSH and high FT4 or FT3 suggest an overactive thyroid.
• A slightly raised TSH with a normal FT4 is called subclinical hypothyroidism. Doctors often wait and see rather than treat it straight away.

Normal ranges vary between laboratories, and TSH naturally rises in people over 70. Illness, some medicines (including the contraceptive pill, steroids, lithium and amiodarone) and supplements containing iodine or biotin can also affect your results. Share your results with a doctor, who can look at them alongside your symptoms.

A thyroid storm is a rare but life-threatening complication of an overactive thyroid. Call 999 if you think you or someone you’re with is having a thyroid storm. Symptoms include a rapid heartbeat, a high temperature, severe agitation or confusion, yellowing of the skin or eyes, and loss of consciousness.

See a doctor if you find a new lump in your neck, or an existing lump is getting bigger. Get urgent medical advice if you have difficulty swallowing or breathing.

Better2Know offers:

• Thyroid Profile: measures TSH, free T4 and free T3 from a blood sample, with results in 1 day. You can book it at one of our clinics or order a home test.
• Comprehensive Thyroid Test: adds thyroid peroxidase and thyroglobulin antibodies to check for an autoimmune cause, with results in 2 days, at one of our clinics.
• Thyroid Profile 1: a home test that measures TSH and free T4, with results in 1 day.

Not sure which test you need? Our Patient Care Team is available 24/7 on 020 7099 0955.

Can a thyroid blood test find thyroid cancer?

Not on its own. A thyroid blood test shows how well your thyroid is working, but thyroid cancer is diagnosed with an ultrasound scan of the neck and a needle biopsy. See a doctor if you notice a lump in your neck.

Can biotin supplements affect a thyroid test?

Yes. High doses of biotin, often sold as a beauty supplement, can give false results that look like an overactive thyroid. The British Thyroid Foundation passes on US advice to stop taking biotin for 2 days before a thyroid test.

Can a thyroid problem affect your sex drive?

It can. The NHS lists an underactive thyroid among the long-term conditions that can lower your sex drive, and an overactive thyroid can cause a loss of interest in sex.

Thyroid problems are common, especially in women, and their symptoms are easy to mistake for something else. If you have symptoms or a higher risk, a simple blood test can give you an answer.

Book a Thyroid Profile at a clinic near you or order a home test kit. Our Patient Care Team is available 24/7 on 020 7099 0955.

Not in the UK? Choose your country from the selector at the top of the page for local tests and prices.

This article originally appeared on 12 May 2023 and was last updated on 1 October 2026.

This article is general information and not a substitute for personal medical advice.

Sources

1. NHS, Underactive thyroid (hypothyroidism), reviewed 28 April 2025. https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/
2. NHS, Overactive thyroid (hyperthyroidism), reviewed 11 April 2023. https://www.nhs.uk/conditions/overactive-thyroid-hyperthyroidism/
3. NHS, Overactive thyroid: symptoms, reviewed 11 April 2023. https://www.nhs.uk/conditions/overactive-thyroid-hyperthyroidism/symptoms/
4. NHS, Overactive thyroid: causes, reviewed 11 April 2023. https://www.nhs.uk/conditions/overactive-thyroid-hyperthyroidism/causes/
5. NHS, Overactive thyroid: complications, reviewed 11 April 2023. https://www.nhs.uk/conditions/overactive-thyroid-hyperthyroidism/complications/
6. NHS, Low sex drive (loss of libido), reviewed 26 May 2026. https://www.nhs.uk/symptoms/loss-of-libido/
7. NHS, Infertility: causes, reviewed 9 August 2023. https://www.nhs.uk/conditions/infertility/causes/
8. NHS, Thyroid cancer: symptoms, reviewed 18 May 2023. https://www.nhs.uk/conditions/thyroid-cancer/symptoms/
9. NHS, Thyroid cancer: tests and next steps, reviewed 18 May 2023. https://www.nhs.uk/conditions/thyroid-cancer/tests-and-next-steps/
10. UK National Screening Committee, Thyroid disease (adults), archived March 2022. https://view-health-screening-recommendations.service.gov.uk/thyroid-disease/
11. British Thyroid Foundation, Thyroid function tests, updated 17 September 2026. https://www.btf-thyroid.org/thyroid-function-tests
12. British Thyroid Foundation, Thyroid function testing, updated 21 January 2025. https://www.btf-thyroid.org/thyroid-function-testing
13. British Thyroid Foundation, Thyroid antibodies explained, updated 5 November 2025. https://www.btf-thyroid.org/thyroid-antibodies-explained
14. British Thyroid Foundation, Subclinical thyroid disease, updated 23 January 2025. https://www.btf-thyroid.org/subclinical-thyroid-disease
15. British Thyroid Foundation, Your thyroid gland, updated 26 May 2026. https://www.btf-thyroid.org/what-is-thyroid-disorder
16. British Thyroid Foundation, Pregnancy and fertility in thyroid disorders, updated 17 September 2026. https://www.btf-thyroid.org/pregnancy-and-fertility-in-thyroid-disorders
17. British Thyroid Foundation, Postpartum thyroiditis, updated 23 October 2025. https://www.btf-thyroid.org/postpartum-thyroiditis1
18. British Thyroid Foundation, Diets and supplements for thyroid disorders, updated 14 April 2026. https://www.btf-thyroid.org/diets-and-supplements-for-thyroid-disorders
19. British Thyroid Foundation, Thyroid cancer overview, updated 30 March 2026. https://www.btf-thyroid.org/thyroid-cancer-overview