Thyroglobulin Antibodies
Antibodies aimed at thyroglobulin, a protein made in the thyroid. They are linked to autoimmune thyroid conditions and affect thyroglobulin testing.
AI-drafted. Awaiting verificationAlso called TgAb, Anti-Tg, Tg AbLOINC 8098-6
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What it is
Thyroglobulin is a large protein made by the thyroid, and the gland stores its hormones attached to it. In autoimmune thyroid conditions, the immune system can make antibodies against thyroglobulin. This test measures how much of these antibodies is in your blood. It is sometimes ordered with TPO antibodies. It is also used after thyroid cancer treatment, because these antibodies can make a thyroglobulin test read falsely low.
Why it matters
A positive result is linked to autoimmune thyroid conditions such as Hashimoto's thyroiditis, but it does not show how well your thyroid is working. TSH and free T4 do that. About one in ten people in the US with no known thyroid disease have a positive result, so a positive result alone is not specific. If you have been treated for thyroid cancer, TgAb matters for another reason. When present, it can make thyroglobulin, the tumor marker, read falsely low or undetectable. Guidelines say it should be measured with every thyroglobulin test, and clinicians follow whether it is falling or rising over time.
If it’s high
An antibody level above your lab's cutoff is reported as positive. It is linked to autoimmune thyroid conditions, most often Hashimoto's thyroiditis. Many people with a positive result have normal thyroid function. After thyroid cancer treatment, a rising level is something your clinician follows closely.
Common causes
- No known thyroid disease: about 1 in 10 people in a US survey (10.4%) had positive TgAb
- Being a woman or being older: positive results are more common in women and become more common with age
- Hashimoto's thyroiditis, the most common autoimmune thyroid condition
- Other autoimmune thyroid conditions, such as Graves' disease
- Thyroid cancer (the common, differentiated types): about 1 in 4 people with it have TgAb at diagnosis or during treatment
- A temporary rise after thyroid surgery or radioactive iodine treatment
What can help
- Ask how often your TSH should be checked
- Ask whether TPO antibodies, TSH and free T4 are needed alongside this result
- If you have been treated for thyroid cancer, ask how TgAb and thyroglobulin will be followed, and whether the same lab and method will be used each time
- Tell your clinician if you are pregnant or planning to be, and about any other autoimmune conditions
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
For adults: 0–4 IU/mL. Source: ARUP Laboratories, Labcorp.
- Adults (this one applies)0–4 IU/mL
Sources: ARUP Laboratories, Labcorp
If this applies to you
TgAb means a little more for some people. Open the one that fits you.
Thyroid condition
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.
What can affect your result
- Sex: positive results are more common in women
- Age: positive results become more common with age
- Test method: cutoffs and calibration differ between labs, so results are not interchangeable
- Thyroid surgery or radioactive iodine treatment, which can temporarily raise levels
- Biotin supplements, on some immunoassays
- High-dose biotin can interfere with some immunoassays. Labcorp asks patients to stop biotin at least 72 hours before the draw; Mayo Clinic Laboratories asks for 12 hours without biotin before its thyroglobulin-related tests. Check with your clinician or lab first.
- Results from different assays are not interchangeable, because cutoffs and calibration differ between methods. For follow-up, use the same method each time (ATA 2015).
- Thyroid surgery and radioactive iodine treatment can make TgAb rise for a while (ATA 2015).
- Some labs print only Positive or Negative, and a few use an equivocal band.
Antibody levels change slowly, over months to years. After total thyroidectomy and radioiodine ablation, TgAb usually disappears over a median of about 3 years in people without persistent disease (ATA 2015).
When to talk to a clinician
A positive result is not urgent by itself. Talk with a clinician about what it means alongside your TSH and free T4, especially if you have unusual tiredness, feeling cold, constipation, weight changes, a racing heart or swelling at the front of the neck. If you have had thyroid cancer and your TgAb level is rising, contact the clinician who follows your thyroid care.
Questions you could ask
- Will the same lab and method be used each time, so my results can be compared?
- If I have had thyroid cancer, how will TgAb and thyroglobulin be followed together?
- What does this result mean for my thyroid, given my TSH and free T4?
- Should TPO antibodies be checked too?
- How often should we recheck my TSH?
Questions people ask
What does a positive thyroglobulin antibody result mean?
It means your immune system has made antibodies against thyroglobulin, a protein in the thyroid. This is linked to autoimmune thyroid conditions such as Hashimoto's thyroiditis, but about 1 in 10 people with no known thyroid disease are also positive. It does not show how well your thyroid is working right now, so your clinician reads it together with your TSH and free T4.
Why is TgAb checked with a thyroglobulin test?
After thyroid cancer treatment, thyroglobulin is followed as a marker. TgAb can make that marker read falsely low, so guidelines say both should be measured together. A rising TgAb level is also followed over time.
Why do different labs use different cutoffs?
TgAb tests are made by different manufacturers, and each one sets its own cutoff. A result that is positive on one method can be negative on another. Compare your number with the cutoff printed on your own report.
Show the science and sources
Units
- 1 IU/mL = 1 IU/mL
- 1 IU/mL = 1 kIU/L
Is a change real?
TgAb naturally varies about 8.5% from test to test in the same healthy person. Between two results from the same lab, a rise of 41% or more, or a fall of 29% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Biological variation estimates of thyroid related measurands - meta-analysis of BIVAC compliant studies (Fernandez-Calle P et al., EFLM WG-BV).
For clinicians and researchers
Thyroglobulin (Tg) is the iodinated glycoprotein on which thyroid hormone is synthesized and stored. TgAb are detected by immunoassay; Labcorp and ARUP both use Beckman Coulter methods, and Mayo uses an immunoenzymatic assay. ARUP does not recommend the test in the initial evaluation of autoimmune thyroid disease and uses it mostly to judge whether thyroglobulin results in thyroid cancer are reliable, while Labcorp lists it to detect and confirm autoimmune thyroiditis. Positivity cutoffs are assay-specific: ARUP 4.0 IU/mL or less is negative, Mayo is under 1.8 IU/mL, and Labcorp flags anything above its limit of detection. Labcorp states that screened young men with TSH 0.5 to 2.0 mIU/L and no thyroid or autoimmune disease had a 95% nonparametric upper reference limit below 4 IU/mL, and 96% of 519 screened adults fell below 4 IU/mL. In NHANES III, TgAb were positive in 10.4 +/- 0.5% of people without known thyroid disease, more often in women and increasing with age. TgAb alone, without TPO antibodies, was not significantly associated with thyroid disease (Hollowell 2002). TgAb occur in about 25% of differentiated thyroid cancer patients. Their presence falsely lowers serum Tg measured by immunometric assay, so ATA 2015 says TgAb should be measured together with every serum Tg test. Although standardization to International Reference Preparation 65/93 has been recommended, assay variability remains wide. Serial TgAb with the same method serve as an imprecise surrogate for residual thyroid tissue or tumor, and falling levels suggest a good response while rising levels are linked to higher recurrence risk (ATA 2015; Spencer and Fatemi 2013). Mayo evaluates suspected heterophile interference with Tg using an interference profile that includes TgAb.
LOINC 8098-6 (primary), 56536-6, 15210-8. Specimen: serum-or-plasma.
Sources
- Thyroglobulin Antibody (test 0050105), ARUP Laboratories
- Thyroglobulin Antibody (test 006685), Labcorp
- Thyroglobulin Antibody, Serum (Non-Orderable) (TGABI), Mayo Clinic Laboratories (Extended Catalog)
- Serum TSH, T4, and thyroid antibodies in the United States population (1988 to 1994): NHANES III, Journal of Clinical Endocrinology & Metabolism (2002)
- 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer: The American Thyroid Association Guidelines Task Force on Thyroid Nodules and Differentiated Thyroid Cancer, Thyroid (American Thyroid Association) (2016)
- Thyroglobulin antibody (TgAb) methods - Strengths, pitfalls and clinical utility for monitoring TgAb-positive patients with differentiated thyroid cancer, Best Practice & Research Clinical Endocrinology & Metabolism (2013)
AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.