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Thyroglobulin (Tg)

A protein made only by thyroid cells. It is mainly used after thyroid cancer treatment as a tumor marker, and it is not a test for diagnosing cancer.

AI-verified against cited sources. Awaiting expert reviewAlso called TgLOINC 3013-0

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What it is

Thyroglobulin (Tg) is a large protein made by thyroid cells. Your thyroid uses it to build and store thyroid hormone. A small amount leaks into the blood, and the amount roughly follows how much thyroid tissue you have. After the thyroid is removed and treated for thyroid cancer, very little Tg should be left, so care teams track it as a tumor marker. It is usually checked along with thyroglobulin antibodies, because those can interfere with the result.

Why it matters

If you still have a thyroid, Tg is not a useful test for finding cancer, because many ordinary thyroid conditions raise it. After thyroid cancer treatment, the trend matters. A very low or undetectable level is what care teams hope for, and a level that rises is a reason to look further. Results depend on the lab method and on whether thyroglobulin antibodies are present, so it works best when the same lab and method are used each time.

If it’s low

A low or undetectable Tg is what care teams expect after the thyroid has been removed and treated, and they look for it to stay very low over time. In someone who still has a thyroid, a low Tg usually does not point to a specific problem. One caution: thyroglobulin antibodies can hide Tg on some tests, so a low result is only reassuring if antibodies were checked.

Common causes

  • Thyroid removed and treated, which is the goal after thyroid cancer treatment
  • Thyroid hormone medicine, which lowers TSH and so lowers Tg
  • Thyroglobulin antibodies, which can make Tg look lower than it is
  • Differences between test methods

What can help

  • Ask whether thyroglobulin antibodies were measured at the same time
  • Ask whether a method that is less affected by antibodies, such as mass spectrometry, is available

If it’s high

A Tg above your lab's range can come from many ordinary thyroid conditions. If you have been treated for thyroid cancer, a Tg that stays detectable or keeps rising is a reason for your care team to look further, though it does not always mean cancer has returned. Your care team reads it along with your history, other tests and your TSH.

Common causes

  • A goiter, thyroid nodules or an enlarged thyroid
  • Graves' disease or another cause of an overactive thyroid
  • Thyroiditis, an inflammation of the thyroid
  • Thyroid tissue left behind after surgery, which is common
  • A raised TSH, for example from low iodine intake or from being off thyroid hormone before a stimulated test
  • A recent thyroid biopsy, surgery or neck injury
  • Thyroid cancer, or its return after treatment
  • Rarely, a lab interference (heterophile antibodies) that gives a falsely high result

What can help

  • Ask how this result compares with your earlier ones on the same method
  • Ask whether thyroglobulin antibodies were checked
  • Ask whether the lab can check for interference if the result does not fit the rest of the picture

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: 0–33 ng/mL. Source: Mayo Clinic Laboratories, via the Mayo Clinic Laboratories extended catalog, Clinical Chemistry and Laboratory Medicine, World Journal of Biological Chemistry, Journal of the Endocrine Society, MedlinePlus (NIH National Library of Medicine), Thyroid (American Thyroid Association), Endocrinology and Metabolism, BMC Cancer.

If this applies to you

Thyroglobulin means a little more for some people. Open the one that fits you.

Thyroid condition

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.

Blood tests for a thyroid condition

What can affect your result

  • How much thyroid tissue you have: a whole thyroid, a remnant or none
  • TSH level: on thyroid hormone treatment, or raised or stimulated
  • Thyroglobulin antibodies, which can lower results on some tests
  • Heterophile antibodies, which can raise results
  • Test method, sensitivity and lab
  • Iodine intake and smoking
  • Sex: levels were higher in women in one reference study
  • Biotin supplements
  • A recent thyroid biopsy or surgery
  • Thyroglobulin antibodies can make results on some tests look lower than they really are, so Tg is usually ordered together with an antibody test.
  • Heterophile (assay-interfering) antibodies can cause a falsely high result. Mayo Clinic Laboratories offers an interference evaluation that compares the immunoassay with other approaches, including mass spectrometry.
  • Biotin: Mayo Clinic Laboratories asks people to avoid supplements containing biotin (vitamin B7) for 12 hours before the draw.
  • Different Tg assays give different numbers, so results should be compared only from the same lab and method.
  • Thyroid hormone treatment lowers TSH and so lowers Tg, while a raised or stimulated TSH raises it. Your care team notes which state you were in.
  • A thyroid needle biopsy or surgery can release Tg into the blood. One review suggests drawing before a needle biopsy or about 2 weeks after, though it says no strong evidence supports this.

Tg has a half-life of about 65 hours (close to 3 days), so after thyroid surgery it falls over weeks. One review says a level 3 to 4 weeks after surgery reflects how much thyroid tissue remains.

When to talk to a clinician

There is no universal urgent cutoff for Tg. If you have had thyroid cancer, contact your care team about a Tg that keeps rising on repeat tests, or if you notice a new lump in your neck, trouble swallowing or a hoarse voice that does not go away. If you have chest pain, trouble breathing or fainting, call 911 or your local emergency number.

Questions you could ask

  • Which Tg method does my lab use, and will future tests use the same one?
  • How often should my thyroglobulin be checked?
  • How does this compare with my earlier results on the same method?
  • Were thyroglobulin antibodies checked?
  • Should we repeat the test or add other tests to put it in context?
  • Were thyroglobulin antibodies checked in case they affect this result?

Questions people ask

Why is my thyroglobulin low or undetectable after thyroid surgery? Is that good?

After the thyroid is removed and treated, there is little or no tissue left to make thyroglobulin, so very low or undetectable is what care teams usually hope to see. Your care team will read it together with your treatment history, other tests and thyroglobulin antibodies.

Why do I need a thyroglobulin antibody test with my thyroglobulin?

Antibodies against thyroglobulin can attach to it and make levels look lower than they really are on some tests. If antibodies are present, thyroglobulin alone may not be a reliable marker, and your care team may follow the antibody level or use other tests.

Can I compare my result with one from a different lab?

Often not directly. Labs use different methods, and the numbers can differ. It is best to have repeat tests at the same lab on the same method. If your lab or method changes, ask your care team how to compare the new result with the old ones.

Show the science and sources

Units

  • 1 ng/mL = 1 ng/mL
  • 1 ng/mL = 1 µg/L

Is a change real?

Thyroglobulin naturally varies about 10.7% from test to test in the same healthy person. Between two results from the same lab, a rise of 39% or more, or a fall of 28% 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

Tg is a large glycoprotein made by thyroid follicular cells and serves as the precursor and storage form of T4 and T3. Serum Tg is proportional to the amount of thyroid tissue, roughly 1 ng/mL per gram when TSH is normal and about half that under TSH suppression, and it rises with TSH stimulation. Half-life is about 65 hours (close to 3 days). Its sensitivity and specificity as a screening test for thyroid cancer are poor, because benign thyroid disease raises it as well. In thyroid cancer follow-up after total thyroidectomy and radioactive iodine, interpretation depends on whether blood was drawn on thyroid hormone or after TSH stimulation, and on anti-Tg antibodies. Open-access studies summarizing the ATA 2015 guideline define an excellent response as Tg below 0.2 ng/mL on thyroid hormone treatment, an indeterminate response as 0.2 to 1 ng/mL, and a biochemical incomplete response as above 1 ng/mL on treatment or above 10 ng/mL after stimulation (or rising antibody levels). These categories apply only to treated thyroid cancer and are not encoded as ranges here. Anti-Tg antibodies are associated with lower measured Tg, but a large 2026 laboratory study found that Tg recovery testing was neither precise enough to detect that interference in a single sample nor specific for it, and the effect sizes were small. Mass spectrometry (for example Mayo's immunocapture LC-MS/MS) is used to check immunoassay results for heterophile interference. Reference limits are assay-specific: Mayo 33 ng/mL or less, Roche Elecsys Tg II 3.5 to 77 µg/L, and Beckman Access 1.4 to 29.2 (men) and 1.5 to 38.5 (women) ng/mL in a healthy reference sample. Because ng/mL and µg/L are numerically identical, no conversion is needed.

LOINC 3013-0 (primary), 14918-7. Specimen: serum.

Sources

  1. Interference Evaluation Heterophile, Thyroglobulin Tumor Marker, Serum (test IETG), Mayo Clinic Laboratories, via the Mayo Clinic Laboratories extended catalog
  2. Thyroglobulin, Tumor Marker, Fine-Needle Aspiration Biopsy Needle Wash (test TFNAB), Mayo Clinic Laboratories, via the Mayo Clinic Laboratories extended catalog
  3. Thyroglobulin Test, MedlinePlus (NIH National Library of Medicine)
  4. Serum thyroglobulin reference values according to NACB criteria in healthy subjects with normal thyroid ultrasound, Clinical Chemistry and Laboratory Medicine (2012)
  5. Use of thyroglobulin as a tumour marker, World Journal of Biological Chemistry (2017)
  6. Critical appraisal of the influence of antithyroglobulin on the measurement of thyroglobulin and thyroglobulin recovery, Journal of the Endocrine Society (2026)
  7. 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer, Thyroid (American Thyroid Association) (2016)
  8. Comparison of Ultrasensitive and Highly Sensitive Assay to Predict Stimulated Thyroglobulin Levels Using Unstimulated Levels in Differentiated Thyroid Cancer Patients, Endocrinology and Metabolism (2025)
  9. Disease status stratification individualizes radioiodine therapy for differentiated thyroid cancer: a prospective, multicenter, real-world study, BMC Cancer (2026)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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