Change of Serum Antithyroglobulin Antibody Levels Is Useful for Prediction of Clinical Recurrence in Thyroglobulin-Negative Patients with Differentiated Thyroid Carcinoma

Objectives: The aim of the study was to evaluate the usefulness of the antithyroglobulin autoantibody (TgAb) value at 6-12 months after remnant ablation in predicting recurrence in differentiated thyroid carcinoma patients who had undetectable thyroglobulin (Tg) values. The change in TgAb concentration measured between the time of remnant ablation (TgAb1) and 6-12 months thereafter (TgAb2) was also evaluated as a possible prognostic indicator. Patients and Methods: Patients with differentiated thyroid carcinoma who underwent total thyroidectomy followed by I-131 remnant ablation between 1995 and 2003 at the Asan Medical Center (Seoul, Korea) were enrolled. Of these, 824 patients with undetectable Tg at 6-12 months after remnant ablation during thyroid hormone withdrawal were the subjects of this study. Results: TgAb2 was positive in 56 patients. Ten of 56 patients (18%) with positive TgAb2 had recurrence, whereas only 10 of 768 patients (1%) with negative TgAb2 had recurrence during 73.6 months of follow-up (P < 0.001). The change between TgAb1 and TgAb2 levels was evaluated in patients with positive TgAb2. TgAb concentration decreased by more than 50% in 21 patients (group 1) and by less than 50% in 16 patients (group 2), and it increased in 19 patients (group 3). The recurrence rates in groups 1, 2, and 3 were 0, 19, and 37%, respectively (P = 0.016). Conclusions: Serum TgAb levels measured at 6-12 months after remnant ablation could predict recurrence in patients with undetectable Tg values. In patients with undetectable Tg and positive TgAb values, a change in TgAb concentration during the early postoperative period may be a prognostic indicator of recurrence. (J Clin Endocrinol Metab 93: 4683-4689, 2008)