Blood tests for a thyroid condition
For people with Hashimoto's, an underactive or overactive thyroid, Graves' disease, or anyone taking thyroid medicine.
10 tests explainedAI-verified against cited sources. Awaiting expert reviewLast reviewed 2026-10-19
For most people with a thyroid condition, TSH is the main number, read together with free T4. Thyroid antibodies help explain the cause, and some only need measuring once. Thyroid results take weeks to settle after a dose change, and a few everyday things can skew them, so testing at a steady time makes your trend easier to read.
The tests that matter most
Most important first. Each one links to its full page, where the note for this group sits near the top.
TSH (Thyroid Stimulating Hormone)
TSH is the main number used to check whether thyroid hormone treatment is at the right level. The ATA suggests rechecking it 4 to 6 weeks after any dose change. Once results are steady, NICE suggests checking about once a year.
Sources: American Thyroid Association (2014) and National Institute for Health and Care Excellence (2019)
- Usual adult range
- 0.45–4.5 mIU/L
Free T4 (Free Thyroxine)
Free T4 is the main thyroid hormone itself, and it is read together with TSH. NICE suggests adding it when symptoms continue after starting levothyroxine. In Graves' disease it helps show early progress, because TSH can stay low for months.
Sources: National Institute for Health and Care Excellence (2019) and European Thyroid Association (2018)
- Usual adult range
- 0.82–1.77 ng/dL
Free T3 (Free Triiodothyronine)
Free T3 is mostly used for an overactive thyroid. NICE suggests checking TSH, free T4 and free T3 every 6 weeks on antithyroid medicine until TSH is back in range. For people taking levothyroxine, the ATA calls TSH the most reliable guide to the dose.
Sources: National Institute for Health and Care Excellence (2019) and American Thyroid Association (2014)
- Usual adult range
- 2–4.4 pg/mL
Thyroid Peroxidase Antibodies (TPO)
TPO antibodies are a sign of thyroid autoimmunity. NICE suggests measuring them once when TSH is raised, and not repeating them. When TSH is only mildly raised, raised thyroid antibodies are one of the things NICE weighs in deciding whether to treat and how often to recheck.
Source: National Institute for Health and Care Excellence (2019)
- Usual adult range
- 0–34 IU/mL
TSH Receptor Antibodies (TRAb / TBII)
TSH receptor antibodies are the main blood sign of Graves' disease. The European guideline suggests measuring them before antithyroid medicine is stopped, since normal levels go with a better chance of remission, and early in pregnancy for anyone with a history of autoimmune thyroid disease.
Sources: European Thyroid Association (2018) and National Institute for Health and Care Excellence (2019)
- Usual adult range
- 0–1.75 IU/L
Thyroid Stimulating Immunoglobulin (TSI)
TSI tests are meant to pick up the stimulating kind of TSH receptor antibody, the kind that switches the thyroid on. The European guideline says cell-based tests for stimulating antibodies help predict thyroid problems in a baby during pregnancy, and effects of Graves' disease outside the thyroid, such as eye changes.
- Usual adult range
- 0–0.55 IU/L
LDL Cholesterol
NICE lists an underactive thyroid among the common causes of unhealthy cholesterol levels, and suggests a TSH test before cholesterol treatment in people with thyroid symptoms. In trials, changing the levothyroxine dose changed cholesterol levels.
Sources: National Institute for Health and Care Excellence (2023) and American Thyroid Association (2014)
- Usual adult range
- up to 99 mg/dL
Thyroglobulin (Tg)
After thyroid cancer treatment, thyroglobulin is followed as a tumor marker. The ATA suggests checking it every 6 to 12 months during early follow-up, in the same lab with the same method each time.
- Usual adult range
- 0–33 ng/mL
Thyroglobulin Antibodies
These antibodies matter most after thyroid cancer treatment. They can make the thyroglobulin result read falsely low, so the ATA advises measuring them with every thyroglobulin test. Falling levels over time are a good sign. A steady rise, or antibodies that newly appear, is linked to a higher chance of the cancer coming back, though levels can rise for a while after surgery or radioactive iodine.
- Usual adult range
- 0–4 IU/mL
Neutrophils (Absolute)
Antithyroid medicine can rarely cause a sharp drop in neutrophils, the white cells that fight infection. NICE suggests a blood count before starting, but not routine counts after that. Guidelines suggest a white cell count if fever or a sore throat develops while taking it.
Sources: National Institute for Health and Care Excellence (2019) and European Thyroid Association (2018)
- Usual adult range
- 1.4–7 ×10³/µL
Ranges shown are the usual adult ranges labs print. The range on your own report is the one your result is judged against.
Getting results you can compare
- Thyroid results take time to settle after a dose change. The ATA suggests rechecking TSH 4 to 6 weeks later. NICE notes that when TSH was very high before treatment, it can take up to 6 months to come back into range.
Sources: American Thyroid Association (2014) and National Institute for Health and Care Excellence (2019)
- If you take levothyroxine, free T4 has a short peak about 15% higher around 4 hours after a dose, the ATA notes. So a draw soon after a dose can read higher. Your clinician can tell you whether to take that day's dose before or after the draw.
- Biotin from supplements can make thyroid results read falsely high or low, and a sudden illness can shift them too, NICE says. Tell your clinician or lab about any biotin you take.
Source: National Institute for Health and Care Excellence (2019)
- After thyroid cancer treatment, thyroglobulin and its antibodies differ between test methods. The ATA advises using the same lab and the same method each time, so results can be compared.
Good to know
- Pregnancy changes thyroid targets. TSH ranges are set for each trimester, and people already taking levothyroxine typically need a higher dose early in pregnancy. The ATA suggests checking TSH every 4 weeks in the first half of pregnancy.
Sources: American Thyroid Association (2014) and American Thyroid Association (2017)
- In Graves' disease, TSH often stays low for several months after treatment starts, even when free T4 and free T3 have come down. The European guideline says TSH is not a sensitive guide to early progress, so a low TSH early on can be expected.
- If your TSH is raised but free T4 is normal and it isn't being treated, NICE suggests checking TSH and free T4 once a year when there are signs of an underlying thyroid condition, such as raised thyroid antibodies, and every 2 to 3 years when there aren't.
Source: National Institute for Health and Care Excellence (2019)
Questions you could ask
- When should we recheck my TSH after this dose change?
- Should I take my thyroid medicine before or after the blood draw?
- Which of my thyroid tests need repeating, and which only needed doing once?
- If I'm planning a pregnancy, how would my thyroid testing change?
- Could any supplement I take, such as biotin, affect these results?
Sources
- Thyroid disease: assessment and management (NG145), National Institute for Health and Care Excellence (2019)
- Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement, American Thyroid Association (2014)
- 2018 European Thyroid Association Guideline for the Management of Graves' Hyperthyroidism, European Thyroid Association (2018)
- 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer, American Thyroid Association (2016)
- Cardiovascular disease: risk assessment and reduction, including lipid modification (NG238), National Institute for Health and Care Excellence (2023)
- American Thyroid Association Task Force Updates Guidelines on Thyroid Disease and Pregnancy (Clinical Thyroidology for the Public summary of the 2017 ATA pregnancy guideline), American Thyroid Association (2017)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-19. How we build and check these pages.
Educational information, not medical advice. Blood Test Tracker doesn’t diagnose or treat, and it doesn’t replace your clinician. Talk with your clinician before changing medications, supplements or care.