Thyroglobulin Test

The Thyroglobulin (Tg) test measures a protein produced exclusively by thyroid follicular cells that serves as the storage matrix for thyroid hormones T3 and T4. While small amounts are normally present in the blood, the test is not used to assess thyroid function.

Its primary role is as a tumor marker for differentiated thyroid cancers, particularly Papillary Thyroid Carcinoma (PTC) and Follicular Thyroid Carcinoma (FTC), which retain the ability to produce thyroglobulin.

Following total thyroidectomy and radioactive iodine (RAI) ablation, thyroglobulin levels should become undetectable. A detectable or rising Tg level may indicate persistent, recurrent, or metastatic thyroid cancer, making it a highly sensitive tool for post-treatment monitoring and surveillance, rather than initial cancer diagnosis.

Who should get this test done?

This test is recommended for individuals who:

●     Require assessment of residual thyroid tissue after thyroid cancer surgery.

●     Are high-risk thyroid cancer patients requiring closer follow-up.

●     Are being evaluated for suspicious thyroid nodules or masses.

●     Are newborns with abnormal TSH screening results to help assess congenital hypothyroidism.

●     Have unexplained neck masses or lymphadenopathy in the context of prior thyroid disease.

Why consider this test?

The Thyroglobulin (Tg) test is a key tool in thyroid cancer follow-up and management. It helps:

●     Detect thyroid cancer recurrence after treatment, often before symptoms or imaging findings appear.

●     Monitor treatment response through serial Tg measurements over time.

●     Detect and monitor metastatic thyroid cancer, as Tg levels often correlate with tumor burden.

●     Identify thyroid tissue in unusual locations, such as ectopic thyroid tissue or metastatic deposits.

●     Evaluate congenital hypothyroidism in newborns, helping distinguish thyroid agenesis (absent thyroid tissue) from dyshormonogenesis (thyroid tissue present but hormone production impaired).

More Information

Anti-Thyroglobulin Antibodies (Anti-Tg Abs) can interfere with Tg measurement and cause falsely low or undetectable results; therefore, Anti-Tg antibodies should always be tested alongside thyroglobulin. If Anti-Tg antibodies are present, Tg results may be unreliable, and alternative surveillance methods such as imaging may be required. Test sensitivity improves with TSH stimulation (via thyroid hormone withdrawal or recombinant human TSH), which increases thyroglobulin production from any remaining thyroid or cancer cells. Thyroglobulin is useful only for cancers arising from thyroid follicular cells and is not a marker for Medullary Thyroid Carcinoma or Anaplastic Thyroid Carcinoma. For medullary thyroid cancer, Calcitonin and CEA (Carcinoembryonic Antigen) are the preferred tumor markers.

Other names

●     Tg Test

●     Serum Thyroglobulin Test

●     Thyroglobulin Tumor Marker Test

●     Thyroid Cancer Surveillance Test

●     Tg Tumor Marker

●     Thyroglobulin - Post Thyroidectomy Test

●     Thyroid Cancer Recurrence Marker Test

●     Thyroglobulin Antibody Test (when ordered alongside Anti-Tg)

●     Stimulated Thyroglobulin Test (when performed under TSH stimulation)

●     Thyroglobulin Monitoring Test