Thyroglobulin, Comprehensive (With Anti-Tg Screen and Reflex to RIA) (Endocrine Sciences)

The Thyroglobulin, Comprehensive (with Anti-Tg Screen and Reflex to RIA) test is used for postoperative surveillance of differentiated thyroid carcinoma by selecting the Tg measurement method according to anti-Tg status to reduce autoantibody interference. The anti-Tg screen flags potential Tg immunoassay bias; a positive result triggers reflex Tg by RIA, whereas a negative result permits Tg measurement by ICMA. Identification of anti-thyroglobulin antibodies (Tg Ab; anti-thyroglobulin autoantibodies) also aids the evaluation of autoimmune thyroid disease and informs assessment of thyroid involvement in patients with systemic autoimmunity.

Thyroglobulin is a follicular cell–derived glycoprotein precursor for triiodothyronine (T3) and thyroxine (T4) that is stored in thyroid colloid. Trace quantities reach the circulation and can function as an autoantigen, provoking anti-thyroglobulin autoantibodies (anti-Tg) that may contribute to thyroid inflammation and dysfunction. Anti-Tg antibodies are found in approximately 40% to 70% of individuals with chronic autoimmune thyroiditis, in about 70% of those with hypothyroidism, in roughly 40% of patients with Graves disease, and in a smaller fraction of patients with other autoimmune conditions; low-titer reactivity can also be seen in healthy persons, particularly older women. Anti-Tg may cross-react with orbital connective tissue components and has been implicated in the pathophysiology of thyroid-associated ophthalmopathy. In pregnancies complicated by maternal autoimmune thyroid disease, testing for thyroid autoantibodies at the start and near the conclusion of gestation can help assess the risk of neonatal thyroid dysfunction.