Thyroglobulin antibodies: normal range and high results

Thyroglobulin antibodies (TgAb) are antibodies your immune system makes against thyroglobulin, the protein your thyroid builds its hormones on. A positive result is a sign of thyroid autoimmunity, most often Hashimoto's thyroiditis, the most common cause of an underactive thyroid in the United States.¹² TgAb is also common in healthy people: about 1 in 13 U.S. adults tests positive.³

The short version

• Normal is negative, meaning below your lab's cutoff. Cutoffs vary a lot by test: 0.0–0.9 IU/mL at Labcorp and 4.1 IU/mL or less at OHSU.⁴⁵ The Libby app's optimal range is 1.0 IU/mL or less.⁶
• A positive result usually points to Hashimoto's thyroiditis (60–80% of people with it have TgAb) or Graves' disease (30–60%).² TgAb on its own, with negative TPO antibodies, showed no significant link to thyroid disease in the U.S. national health survey.⁷
• TSH and free T4 show how your thyroid is working. With positive antibodies, the higher the TSH, the higher the odds of an underactive thyroid later: 12% of women at a TSH of 2.5 or less vs 86% above 4.0 over 13 years in one study.⁸
• No TgAb level is an emergency by itself. After thyroid cancer, TgAb has a second job: it can make a thyroglobulin test read falsely low.⁹¹⁰

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What thyroglobulin antibodies are

Thyroglobulin (Tg) is a large protein made by your thyroid cells. The cells pass it into the follicle, a small storage sac inside the gland, where iodine is attached to it. Pieces of that iodine-loaded protein pair up to make the thyroid hormones T4 and T3.¹¹ A small amount of thyroglobulin leaks into your bloodstream.¹² (More on the chemistry at the end.)

Sometimes the immune system makes antibodies against thyroglobulin. Those are TgAb. The American Thyroid Association names them, with TPO (thyroid peroxidase) antibodies, as the two common thyroid antibodies. Positive TPO or Tg antibodies in someone with an underactive thyroid point to Hashimoto's thyroiditis.¹³

Clinicians order TgAb for two reasons. The first is to look for an autoimmune cause when thyroid tests are off or symptoms suggest thyroiditis. The second, after treatment for thyroid cancer, is to check whether a thyroglobulin result can be trusted.¹²⁴

What's a normal TgAb?

A negative result is the normal result.¹² Start with the cutoff printed on your own report, because TgAb tests differ widely:

• Labcorp, a commercial lab, reports 0.0–0.9 IU/mL as the reference interval for its test (a Beckman Coulter method).⁴
• OHSU's test (Abbott Alinity i) calls 4.1 IU/mL or less negative.⁵
• The U.S. national health survey (NHANES) counted 0.4 IU/mL or more as positive in 2007–2012, and 1.0 or more on the older test it used in 1988–1994.³

The American Thyroid Association's laboratory committee notes that TgAb tests agree poorly with each other, so the same blood can be positive on one test and negative on another.⁹ Compare results from the same lab when you can.

Low-level positives are common. Labcorp's report notes that on its test, about 4% of people with no sign of thyroid disease or autoimmunity have TgAb up to 4 IU/mL.⁴ In NHANES 2007–2012, 7.7% of U.S. adults tested positive.³

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Women test positive about twice as often as men (9.9% vs 5.4%), and the share rises with age, from 5.7% at ages 18–24 to 11.2% at 60 and older.³

"Optimal" TgAb: what health optimizers aim for

Longevity clinics and functional-medicine practitioners want TgAb as low as it goes. Here's the ladder, from strictest to loosest. Each rung belongs to a specific test, and the same numbers apply to men and women:

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Why a positive result matters:

• In the Busselton study, 1,184 Australian adults were followed for 13 years. A TgAb above 22 IU/mL best predicted who developed an underactive thyroid, well under that test's upper limit of 55.⁸
• In women with positive TPO or Tg antibodies, the share who became hypothyroid tracked their starting TSH: 12% at 2.5 or less, 55% at 2.5–4.0, and 86% above 4.0.⁸

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Keep "optimal" in perspective. TgAb is a flag for autoimmunity, and TSH and free T4 are what guide treatment. The American Thyroid Association says people with high thyroid antibodies and normal TSH and free T4 need no thyroid hormone, and that repeating antibody levels is unnecessary; TSH is the test to follow.¹ On its own, TgAb carries less weight than TPO antibodies: in NHANES III, TgAb without TPO antibodies showed no significant link to thyroid disease.⁷ Chasing the number with supplements has little support. In a 2024 meta-analysis of 35 studies, selenium lowered TPO antibodies and left TgAb without a significant change.¹⁶

What a positive TgAb usually means

Your other thyroid tests are the first clue. A positive TgAb shows the immune system has reacted to thyroglobulin. TSH, free T4 and TPO antibodies show whether that's affecting the gland.¹³

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The usual suspects:

• Hashimoto's thyroiditis. It's the most common cause of an underactive thyroid in the U.S., and it's most common in women.¹ About 60–80% of people with Hashimoto's have TgAb, and 90–95% of people with autoimmune thyroid disease have TPO antibodies.² Early on, antibodies can be high while thyroid hormone levels are still normal.¹
• Antibodies without thyroid disease. TgAb turns up in about 1 in 13 U.S. adults, more often with age.³ Labcorp notes that at very low levels, TgAb may be neither harmful nor a sign of disease.⁴
• Graves' disease, an overactive thyroid driven by TSH-receptor antibodies (TRAb).¹³ About 90% of people with Graves' have TRAb. Estimates for TgAb range from 30–40% to 50–60%.²
• Less common causes: subacute thyroiditis, type 1 diabetes and lupus. Pregnant women and relatives of people with autoimmune thyroiditis can also test positive.¹² Across non-thyroid immune disorders, about 10–15% have TgAb.²
• Thyroid cancer. About 20% of people with differentiated thyroid cancer have TgAb.¹⁰ Here its main job is flagging a thyroglobulin result that may read falsely low (see Going deeper).⁹

Get prompt care if thyroid symptoms turn severe. A high temperature, a pounding heart, confusion or agitation can mean thyroid storm. A low body temperature, slowed breathing or unresponsiveness can mean myxedema crisis. Both are emergencies.¹⁵

TgAb reads best next to its neighbors

TgAb means most next to the rest of the thyroid panel: TPO antibodies, TSH, free T4 and, when Graves' disease is a question, TRAb.¹³²

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To see how well your thyroid is working, look at TSH and free T4. The antibodies help explain why.¹³

How fast TgAb changes

Slowly. Antibody production continues as long as thyroid tissue is there. When the gland is completely removed, the antibodies fade over months to years.¹⁷

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What that means in practice:

• After thyroid-cancer surgery, TgAb disappeared in a median of 11 months in one series, with most gone by 32 months.¹⁸ After complete removal plus radioiodine, the median was 3 years for TgAb and 6.3 years for TPO antibodies.¹⁷
• In Hashimoto's, rechecking antibodies adds little. The American Thyroid Association says following antibody levels over time is unhelpful for spotting a failing thyroid or judging treatment. TSH and free T4 do that job.¹³
• Stick with one lab. TgAb tests disagree, so a switch of lab can move you across a cutoff with no change in your body.⁹
• Mention biotin. High-dose biotin can interfere with Labcorp's test, and Labcorp asks patients to stop it at least 72 hours before the blood draw.⁴ Check with your clinician first.

Going deeper: thyroglobulin and the Tg test

How thyroglobulin makes hormone. Thyroid cells ship thyroglobulin into the follicle. There, some of its tyrosines (protein building blocks) pick up one or two iodine atoms, becoming MIT or DIT. Two DITs joined together make T4. An MIT plus a DIT makes T3. TSH turns the whole process up.¹¹

Why TgAb matters for the thyroglobulin test. After thyroid-cancer treatment, thyroglobulin in the blood works as a tumor marker. Most labs measure it with a "sandwich" test: one antibody grabs the thyroglobulin and a second one tags it. When your own TgAb is already stuck to the thyroglobulin, the test can miss it, and the result reads falsely low. The size of the error varies from patient to patient and is unrelated to the TgAb level.⁹

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That's why the 2025 American Thyroid Association thyroid-cancer guideline says TgAb should be measured with every thyroglobulin test, that TgAb trends are best read on the same test over time, and that imaging is the main way to follow people who have TgAb.¹⁰ Labs also treat the cutoff differently for this job. Manufacturers set their cutoffs for autoimmune thyroid disease, and those are often too high to catch TgAb that interferes, so the ATA committee recommends each test's lowest reliable measurement level instead.⁹

Questions worth asking

• Which test and cutoff did my lab use, and is my result close to that cutoff?
• Are my TPO antibodies positive too?
• What do my TSH and free T4 show, and how often should we recheck them?
• Do my symptoms fit an underactive or an overactive thyroid?
• Should I pause biotin before my next blood draw?
• If I've had thyroid cancer: was TgAb measured with my thyroglobulin, on the same test as last time?

FAQ

What is a normal thyroglobulin antibody level? Negative, meaning below your lab's cutoff. Cutoffs vary by test, from 0.9 IU/mL at Labcorp to 4.1 IU/mL at OHSU.⁴⁵

Does a positive TgAb mean I have Hashimoto's? It's a common sign of Hashimoto's thyroiditis, and many people with TgAb also have no thyroid disease. TSH, free T4 and TPO antibodies settle the question.¹³⁷

Can TgAb be high with a normal TSH? Yes. Antibodies often appear while thyroid hormone levels are still normal. With normal TSH and free T4, no thyroid hormone treatment is needed; your TSH is the test to follow.¹

Why is TgAb tested with thyroglobulin? TgAb can make a thyroglobulin result read falsely low, so thyroid-cancer guidelines measure it with every thyroglobulin test.¹⁰⁹

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This guide is for education. It can't diagnose you or replace care from a clinician who knows your history.

Footnotes

1. American Thyroid Association. Hashimoto's Thyroiditis. Patient page: the most common cause of hypothyroidism in the U.S.; people with high thyroid antibodies and normal TSH and free T4 need no thyroid hormone, and repeating antibody levels is unnecessary. thyroid.org ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

2. Fröhlich E, Wahl R. Thyroid Autoimmunity: Role of Anti-thyroid Antibodies in Thyroid and Extra-Thyroidal Diseases. Front Immunol. 2017;8:521. Review of how often TgAb, TPO antibodies and TSH-receptor antibodies appear in Hashimoto's, Graves' and other autoimmune diseases. PMC ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

3. Dillon CF, Weisman MH, Miller FW. Population-based estimates of humoral autoimmunity from the U.S. National Health and Nutrition Examination Surveys, 1960–2014. PLoS One. 2020;15(1):e0226516. NHANES TgAb prevalence by age and sex, and the survey cutoffs (under 1.0 IU/mL in 1988–1994, under 0.4 IU/mL in 2007–2012). PMC ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰

4. Labcorp. Test 006685: Thyroglobulin Antibody, with its sample report. A commercial laboratory, cited for its own test's range and instructions. Beckman Coulter method; reference interval 0.0–0.9 IU/mL; report note that 4% of people without thyroid disease or autoimmunity have TgAb up to 4 IU/mL; stop high-dose biotin at least 72 hours before collection. labcorp.com · sample report ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹

5. Oregon Health & Science University Laboratory Services. Thyroglobulin Antibody. Abbott Alinity i method; 4.1 IU/mL or less is negative; critical values N/A. ohsu.edu ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

6. Kharrazian D. Why Do I Still Have Thyroid Symptoms? When My Lab Tests Are Normal. Elephant Press; 2010. ISBN 978-0985690403. Functional-medicine thyroid book credited by the Libby app's marker catalog for the app's TgAb optimal range of 1.0 IU/mL or less (range as recorded in the Libby app's marker catalog; book not opened for this article). ↩ ↩² ↩³

7. Hollowell JG, Staehling NW, Flanders WD, et al. Serum TSH, T(4), and thyroid antibodies in the United States population (1988 to 1994): National Health and Nutrition Examination Survey (NHANES III). J Clin Endocrinol Metab. 2002;87(2):489–499. 17,353 people; TgAb positive in 10.4%; "TgAb alone in the absence of TPOAb is not significantly associated with thyroid disease." PubMed ↩ ↩² ↩³ ↩⁴ ↩⁵

8. Walsh JP, Bremner AP, Feddema P, Leedman PJ. Thyrotropin and thyroid antibodies as predictors of hypothyroidism: a 13-year, longitudinal study of a community-based cohort using current immunoassay techniques. J Clin Endocrinol Metab. 2010;95(3):1095–1104. 1,184 Busselton participants; TgAb above 22 kIU/L best predicted hypothyroidism (reference limit 55 kIU/L). PubMed ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

9. American Thyroid Association Laboratory Services Committee. Thyroglobulin (Tg) Assays. How TgAb makes thyroglobulin tests read low (41–86% across four assays), poor agreement between TgAb tests, and why autoimmune cutoffs are too high for this job. thyroid.org ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰

10. Ringel MD, Sosa JA, Baloch Z, et al. 2025 American Thyroid Association Management Guidelines for Adult Patients with Differentiated Thyroid Cancer. Thyroid. 2025;35(8):841–985. Recommendation 47 (TgAb with every thyroglobulin test, same-assay trends, imaging first); TgAb in about 20% of patients; a median of 15.8 months to turn negative in one cited study. PMC ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

11. Citterio CE, Targovnik HM, Arvan P. The role of thyroglobulin in thyroid hormonogenesis. Nat Rev Endocrinol. 2019;15(6):323–338. How iodinated tyrosines on thyroglobulin couple into T4 and T3. PubMed ↩ ↩² ↩³

12. National Library of Medicine. Antithyroglobulin antibody test. MedlinePlus Medical Encyclopedia. Reviewed January 25, 2026. What the test is, why it's ordered, "a negative test result is a normal result," and the conditions linked to a positive result. MedlinePlus ↩ ↩² ↩³ ↩⁴ ↩⁵

13. American Thyroid Association. Thyroid Function Tests. Patient page: TSH and free T4 patterns, thyroid antibodies, TSI in Graves' disease, and why following antibody levels over time is unhelpful. thyroid.org ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹

14. Superpower. Thyroglobulin antibodies biomarker page. Last updated September 1, 2026. States that thyroglobulin antibodies "absent or undetectable" is optimal. A commercial source, listed as what the optimizer community uses. superpower.com ↩ ↩²

15. National Library of Medicine. Thyroid storm (reviewed January 25, 2026) and Hypothyroidism (myxedema crisis). MedlinePlus Medical Encyclopedia. Symptoms of both emergencies. Thyroid storm · Hypothyroidism ↩ ↩² ↩³

16. Huwiler VV, Maissen-Abgottspon S, Stanga Z, et al. Selenium Supplementation in Patients with Hashimoto Thyroiditis: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. Thyroid. 2024;34(3):295–313. 35 studies; selenium lowered TPO antibodies, with no significant change in TgAb. PubMed ↩

17. Chiovato L, Latrofa F, Braverman LE, Pacini F. Disappearance of humoral thyroid autoimmunity after complete removal of thyroid antigens. Ann Intern Med. 2003;139(5 Pt 1):346–351. 182 patients after total thyroidectomy and radioiodine; median disappearance 3.0 years for TgAb and 6.3 years for TPO antibodies. PubMed ↩ ↩² ↩³

18. Xu J, Bergren R, Schneider D, Chen H, Sippel RS. Thyroglobulin antibody resolution after total thyroidectomy for cancer. J Surg Res. 2015;198(2):366–370. 34 of 247 patients TgAb-positive (20 IU/mL or more); median resolution 11.0 months, most by 32.4 months. PMC ↩ ↩²