Abstract
Background: Despite the excellent prognosis, recurrence rate of differentiated thyroid carcinoma (DTC) is 20%–40%, hence long-term follow-up is needed. Thyroglobulin (Tg) measurement is important for follow up and assessment of recurrence in DTC but in the presence of antiTg autoantibody (ATgAb), a negative Tg result may be false negative. Recent guidelines recommend assessing ATgAb, along with measurement of serum Tg, every 6 12 months post surgery. Persistence of ATgAb after the treatment or increasing concentrations indicates persistent or recurrent DTC.
Methods: A total of 90 patients of DTC who underwent total thyroidectomy along with I-131 ablation, with TSH stimulated Tg < 2 ng/ml were included
in this study. Serial assessment of Tg and ATgAb level was done in these patients. Conclusion were extracted after the comparison of ATgAb level with available imaging modalities, i.e., whole body scan, ultrasound, chest X-ray, bone scintigraphy, CT, and magnetic resonance imaging and response to therapy.
Results: Out of total 90 patients, 43% had increased ATgAb. There was no significant difference in gender (p < 0.48) or multifocality (p < 0.04) between ATgAb positive and negative groups. Compared with ATgAb negative group, a greater number of ATgAb positive patients had lymph nodal metastasis (p < 0.004) and extrathyroidal extension (p < 0.002). Raised ATgAb levels and disease status are very well correlated p < 0.05. Out of 39 patients, 17.98% with positive ATgAb showed recurrence, whereas only 3.92% of 51 patients with negative ATgAb had recurrence during the follow up (p < 0.028). Recurrence rate was (0%) in group I, (10%) in group II, and (45%) in group III.
Conclusion: ATgAb is also a tumor marker, rising when tumor is present and falling when it has been destroyed. There is a statistically significant correlation between the complete disappearance of thyroid tissue and that of ATgAb so serial measurement of ATgAb levels in the follow up of patients of DTC is as important as the measurement of Tg level.

Key words: Thyroid cancer, thyroglobulin, anti-thyroglobulin.