This test measures two antibodies that the immune system can make against the thyroid gland: thyroid peroxidase (TPO) antibodies and thyroglobulin antibodies. They are markers of autoimmune thyroid disease, the most common cause of an underactive thyroid in the UK.
Antibodies show whether an autoimmune process is present. They do not show whether your thyroid is currently making the right amount of hormone, so they are usually interpreted alongside TSH and free T4.
What is measured
- TPO antibodies (anti-thyroid peroxidase)
- Thyroglobulin antibodies (anti-thyroglobulin)
Useful for
- Looking for an autoimmune cause when TSH has been found to be raised
- People with a family history of autoimmune thyroid disease who want results to discuss with their GP
- People with another autoimmune condition, such as type 1 diabetes, discussing thyroid risk with their clinician
Sample: venous blood sample. Fasting: not needed. Biomarkers: 2, both measured. Price includes: laboratory analysis and the laboratory's results report. Interpretation is optional and priced separately.
Thyroid Antibodies Blood Test
- TPO antibodies (measured): the principal marker of autoimmune thyroid disease, used to look for a cause when TSH is raised and to judge the likelihood of future thyroid underactivity.
- Thyroglobulin antibodies (measured): a second marker of thyroid autoimmunity, sometimes positive when TPO antibodies are negative.
The laboratory counts this panel as 2 biomarkers. It does not measure thyroid hormones (TSH, free T4, free T3), TSH receptor antibodies or thyroglobulin itself.
In autoimmune thyroid disease the immune system targets the thyroid's own proteins. Two of these proteins are central to hormone production:
- Thyroid peroxidase (TPO) is the enzyme that attaches iodine during the making of thyroid hormones.
- Thyroglobulin is the large protein inside the thyroid on which the hormones are built and stored.
Antibodies against these proteins are a sign of immune activity directed at the thyroid. In Hashimoto's disease, gradual immune damage can reduce hormone output over time, leading to an underactive thyroid. Lab Tests Online UK reports that TPO antibodies are found in about 95% of people with Hashimoto's thyroiditis and about 90% with primary hypothyroidism, and in around 18% of people with Graves' disease.
The two antibodies are used differently
TPO antibodies are the main antibody test for autoimmune thyroid disease. NICE guideline NG145 suggests considering TPO antibody measurement for adults with a TSH above the reference range.
Thyroglobulin antibodies are also found in autoimmune thyroid disease but are considered less reliable than TPO antibodies for detecting it. Their main specialist use is in people treated for differentiated thyroid cancer, where thyroglobulin is used as a tumour marker and thyroglobulin antibodies can interfere with that measurement. That monitoring is carried out by specialist teams and is not the purpose of this test.
Graves' disease, the most common cause of an overactive thyroid, is confirmed with a different antibody, the TSH receptor antibody (TRAb), which is not included here.
Antibody results are reported as a level with the laboratory's cut-off, above which a result is considered positive. Methods and units differ between laboratories, so results from different laboratories cannot be compared directly. If antibodies are ever monitored, the same method and ideally the same laboratory should be used.
What a positive result can mean
- With a raised TSH or low free T4: supports an autoimmune cause, most often Hashimoto's disease.
- With normal thyroid function: some healthy people have thyroid antibodies, and this becomes more common with age and in women. Most never develop thyroid dysfunction, but the risk is higher than in people without antibodies, so a clinician may suggest checking thyroid function from time to time. Positive antibodies with normal thyroid hormones are not, on their own, a reason for treatment.
- Higher levels are more likely to reflect autoimmune thyroid disease than mild elevations, which can occur in other conditions.
What a negative result can mean
A negative result makes autoimmune thyroid disease less likely but does not exclude it, and it says nothing about current hormone levels. A minority of people with Hashimoto's disease test negative, and other thyroid conditions do not involve these antibodies.
Other points
- Thyroid antibodies are also found more often in people with other autoimmune conditions, including type 1 diabetes, pernicious anaemia, rheumatoid arthritis and lupus.
- NICE advises against repeating TPO antibody tests in adults, and the British Thyroid Foundation notes that repeat TPO and thyroglobulin antibody tests rarely change management. Antibody levels are not used to adjust thyroid medication.
- Antibody tests are immunoassays. NICE advises asking about biotin before thyroid testing, as it can interfere with some immunoassays.
If your results need medical attention you will be advised to see your GP, and with your consent Juvenology can write to them.
Antibody testing is most informative when there is a specific question. Lab Tests Online UK describes it being requested when symptoms or results suggest an underactive thyroid, before starting medicines that can trigger thyroid problems in antibody-positive people (such as lithium or amiodarone, decisions made by the prescriber), and in some pregnancy and fertility contexts under clinical supervision.
People also choose this test if a close relative has Hashimoto's disease or if they live with another autoimmune condition. In these situations a combined picture of antibodies and thyroid hormone levels is usually more useful than antibodies alone.
This test suits adults with a raised TSH who want to know whether an autoimmune cause is likely, and people with a strong family history of thyroid disease or another autoimmune condition who want results to discuss with their GP.
May not be the right choice
- Checking whether your thyroid is under- or overactive: you need a thyroid function test (TSH, free T4 and free T3), which can be taken at the same appointment.
- Suspected Graves' disease: TSH receptor antibodies are the relevant test and are arranged through your GP or specialist.
- Thyroid cancer follow-up: thyroglobulin and antibody monitoring should stay with your specialist team and the same laboratory.
- Repeat testing: if you already know you are antibody positive, repeating the test is rarely useful.
- Pregnancy: speak to your midwife, GP or maternity team about thyroid testing.
Established clinical use: TPO antibodies help to identify autoimmune thyroid disease as the cause of a raised TSH and inform how closely thyroid function is followed.
Population associations: thyroid antibodies become more common with age and are more common in women. At population level, antibody-positive people are more likely to develop an underactive thyroid later. This is a probability across groups, not a forecast for an individual.
Emerging research: the role of thyroid autoimmunity in fertility and pregnancy continues to be studied. Decisions about treatment in pregnancy or when trying to conceive are made by your GP, fertility or maternity team.
What this test cannot tell you: it does not measure thyroid hormone levels, cannot predict when or whether thyroid function will change for you, and does not measure a "biological age". Changes in antibody level are not an established guide to treatment.
- Fasting and timing: not needed; the sample can be taken at any time of day.
- Biotin: tell us if you take biotin or a hair, skin and nail supplement containing it; the laboratory or your clinician can advise whether to pause it.
- Thyroid medication: keep taking it as usual.
- Combining tests: if you have not had recent thyroid function results, consider having them taken in the same sample so the antibodies can be interpreted in context.
Choose how your sample is taken when you book. We confirm the collection option, any collection fee and the expected turnaround time before you book.
- Juvenology Clinic, Maidstone (82 King Street, Maidstone ME14 1BH): Available.
- Partner collection location, including London: Available on request. We confirm availability for your postcode before you book.
- Postal home finger-prick kit: Ask before ordering. We offer a home kit only where the laboratory confirms this test is suitable for a finger-prick sample.
Sample: Venous blood sample (serum); sample tube type confirmed by the laboratory
Collection notes: No fasting or timing requirements. Mention biotin supplements at booking. Can be collected in the same sample as a thyroid function test. A postal finger-prick kit is offered only if the laboratory confirms suitability.
The price of this test covers laboratory analysis and the laboratory's results report. The report lists each result beside the laboratory's reference range.
Beyond the blood test: optional support, priced separately
- Personalised written interpretation report: £50
- General consultation: £50
- Results consultation (results discussion and follow-up advice): £100
- Personalised programme: from £150, after we assess whether a programme suits you
Consultations are with Marina, an NMC-registered nurse with an Executive MSc in Longevity from the Geneva College of Longevity Science. She explains what your results show and how they relate to lifestyle. No prescription service is offered with these tests.
If a result suggests you need medical follow-up, we will recommend that you see your GP and, with your consent, can provide a letter to take with you. A blood test cannot rule out every condition. If you have symptoms, speak to your GP or NHS 111, and call 999 in an emergency.
My antibodies are positive but my thyroid function is normal. What does that mean?
It means there is evidence of thyroid autoimmunity without current thyroid underactivity. Many people stay in this state for years and some never develop a problem. Your GP may suggest periodic thyroid function checks, particularly if you develop symptoms.
Do positive antibodies mean I need treatment?
Not on their own. Treatment decisions are based on thyroid hormone levels, symptoms and clinical circumstances. Current guidance does not recommend thyroid hormone treatment when levels are within the normal range.
Should I retest to see whether my antibody levels have fallen?
Usually not. NICE advises against repeat TPO antibody testing in adults, because antibody levels do not guide treatment.
Does a negative result mean I don't have a thyroid problem?
No. Antibodies are absent in some people with thyroid conditions, and they do not measure hormone levels. A thyroid function test is needed to check how your thyroid is working.
Why are two different antibodies tested?
TPO antibodies are the main marker. Thyroglobulin antibodies are sometimes positive when TPO antibodies are not, so measuring both can add information, although thyroglobulin antibodies are less reliable on their own.
Is interpretation included in the price?
The price covers laboratory analysis and the laboratory's report with reference ranges. You can add an optional personalised written interpretation report (£50) or a results discussion consultation (£100).
- Thyroid disease: assessment and management (NG145). National Institute for Health and Care Excellence, 2019, updated 2023. https://www.nice.org.uk/guidance/ng145
- Thyroid antibodies. Lab Tests Online UK. https://labtestsonline.org.uk/tests/thyroid-antibodies
- Thyroid function tests. British Thyroid Foundation, revised 2026. https://www.btf-thyroid.org/thyroid-function-tests
- Underactive thyroid (hypothyroidism). NHS. https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/
- Overactive thyroid (hyperthyroidism). NHS. https://www.nhs.uk/conditions/overactive-thyroid-hyperthyroidism/
