Thyroid Antibodies (TPO, TgAb, TRAb): What They Tell Your Surgeon
Written by John P. Sabra, MD FACS
Updated September 2026
Educational only. This article is not medical advice. Always consult your physician about your individual situation.
Thyroid antibody tests measure proteins your immune system has made against components of the thyroid gland. Three antibody tests are commonly ordered: TPO (thyroid peroxidase), TgAb (thyroglobulin antibody), and TRAb (TSH receptor antibody). Each one identifies a different aspect of autoimmune thyroid disease, and the results carry specific implications for diagnosis, treatment, and cancer surveillance. Here is what each test means in plain language.
Autoimmune thyroid disease is among the most common autoimmune conditions in humans. The immune system mistakenly produces antibodies against the thyroid gland or its components. Depending on which antibody is dominant, the result can be hypothyroidism (Hashimoto disease), hyperthyroidism (Graves’ disease), or asymptomatic thyroid dysfunction.
The Three Main Antibody Tests
| Antibody | What It Targets | What It Suggests |
|---|---|---|
| TPO antibody | Thyroid peroxidase, an enzyme in thyroid cells. | Hashimoto thyroiditis (most common). Also elevated in some Graves’ disease. |
| TgAb (thyroglobulin antibody) | Thyroglobulin protein, normally made by thyroid cells. | Hashimoto thyroiditis. Critical for cancer surveillance interpretation. |
| TRAb (TSH receptor antibody) | The TSH receptor on thyroid cells. | Graves’ disease. Useful in pregnancy and unclear hyperthyroidism cases. |
TPO Antibody (Thyroid Peroxidase)
TPO antibody is the most common autoimmune thyroid antibody. It is elevated in approximately 90% of patients with Hashimoto thyroiditis and in 70 to 80% of patients with Graves disease. A mildly elevated TPO is also found in approximately 10 to 15% of healthy people, particularly women, and on its own it is not always clinically significant.
The TPO result is used to confirm autoimmune thyroid disease in patients with an abnormal TSH, and to predict future risk of thyroid dysfunction in patients with borderline lab values. A patient with subclinical hypothyroidism and a positive TPO has a higher probability of progressing to overt hypothyroidism over time than a patient with the same TSH and negative antibodies.
TgAb (Thyroglobulin Antibody)
TgAb is commonly elevated alongside TPO in Hashimoto thyroiditis. Its single most important role, though, is in thyroid cancer surveillance. After total thyroidectomy for thyroid cancer, thyroglobulin is used as a tumor marker. When TgAb is also present, it interferes with the thyroglobulin measurement and can produce falsely low values. The TgAb result therefore changes how the thyroglobulin number is interpreted.
⚕ Clinical note Approximately 20 to 25% of thyroid cancer patients have detectable TgAb. For these patients, the trend of TgAb levels over time becomes an indirect surveillance marker, on top of the thyroglobulin value itself. A falling TgAb over time is reassuring. A rising TgAb can indicate recurrent disease even when the thyroglobulin appears stable. Every thyroglobulin should be paired with a TgAb.
TRAb (TSH Receptor Antibody)
TRAb is the antibody specific to Graves disease. It binds to and activates the TSH receptor on thyroid cells, driving the gland to produce excess hormone. TRAb is elevated in approximately 95% of patients with active Graves disease and is the most useful single antibody test for diagnosing Graves.
TRAb has specific clinical uses beyond diagnosis. In pregnancy, a high maternal TRAb level can cross the placenta and affect the fetal thyroid, so the level is measured in pregnant women with Graves disease. In patients with unclear hyperthyroidism, where it is uncertain whether Graves disease, a toxic nodule, or thyroiditis is the cause, TRAb helps clarify the diagnosis. After Graves treatment with antithyroid medication, a falling TRAb predicts a higher probability of sustained remission after stopping the medication.
When to Order Antibody Testing
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Abnormal TSH with unclear cause: Antibodies help distinguish autoimmune from non-autoimmune disease.
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New diagnosis of hyperthyroidism: TRAb confirms Graves disease.
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New diagnosis of hypothyroidism: TPO confirms Hashimoto disease.
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Pregnant women with prior or current Graves disease: TRAb predicts neonatal thyroid risk.
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Thyroid cancer surveillance: TgAb at every surveillance visit.
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Family history of autoimmune thyroid disease: To assess risk in patients with borderline thyroid lab values.
⚕ Clinical note Antibody levels do not need to be rechecked routinely once the diagnosis is established. For Hashimoto disease in particular, repeating TPO antibodies year after year adds little. The exception is TgAb in thyroid cancer patients, which is tracked at every surveillance visit because it serves as a tumor marker.
The Bottom Line
Thyroid antibodies are useful tests for diagnosing autoimmune thyroid disease, predicting future thyroid dysfunction, and interpreting cancer surveillance results. TPO confirms Hashimoto disease in most cases. TgAb is essential for interpreting thyroglobulin in cancer surveillance. TRAb is the test for Graves disease. Mildly positive antibodies in otherwise healthy individuals are common and not always clinically significant.
If you have abnormal thyroid function tests, ask whether thyroid antibodies have been checked and what the specific results suggest about the underlying cause.
This article is intended for patient education only. It does not constitute medical advice and does not replace a consultation with your physician. Individual patient circumstances and clinical judgment determine the appropriate evaluation and management for every patient.
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