Thyroglobulin (Tg) is a protein synthesized and used in the thyroid gland. In some disorders, thyroglobulin is synthesized in excess and released outside the thyroid gland. Thyroglobulin testing is now commonly used to monitor the effectiveness and detect recurrence of differentiated thyroid cancer.

Tg and antiTg tests are not used to diagnose thyroid cancer, this test is only valuable for monitoring the disease after treatment for well-differentiated thyroid cancer.