Anti-thyroglobulin Antibody Positivity During Follow-Up of a Patient with Differentiated Thyroid Cancer

Abstract

Serum thyroglobulin (Tg) measurement is the most important and sensitive marker of persistent and/or recurrent disease in the follow-up of differentiated thyroid cancer (DTC) after total thyroidectomy and radioiodine ablation of remnant tissue. However, in the presence of increased level of serum anti-thyroglobulin antibody (TgAb), serum Tg cannot be used reliably as a tumor marker of DTC. On the follow-up of patients with DTC, the standard and useful practice is measuring the levels of both Tg and TgAb. The main source of TgAb positivity is lymphocytic infiltration of thyroid tissue. The increased level of TgAb is also associated with continuing lymphocytic memory cell reply or a low load of thyroid remnant. In patients with a preexisting autoimmune thyroid disease, most of them lose their TgAb positivity during the period up to 2–3 years on follow-up in association with the disappearance of thyroid tissue and its antigenic components after total thyroidectomy and RAI ablation. Therefore, prolonged positive TgAb levels or being positive in follow-up may indicate the recurrent and/or metastatic disease and may be a prognostic indicator of worse outcome. In case of persistent and/or rising TgAb positivity with undetectable Tg levels, especially without preexisting autoimmune thyroiditis, patients must be monitored closely and examined by imaging modalities such as neck ultrasound, and/or CT, MR, and F-18 FDG PET/CT for recurrence.