Postoperative-stimulated serum thyroglobulin measured at the time of 131I ablation is useful for the prediction of disease status in patients with differentiated thyroid carcinoma

Background. This study was conducted to identify the relevant cutoff value and to evaluate the usefulness of postoperative-stimulated serum thyroglobulin (Tg) at the time of I-131 ablation for the prediction of disease status in patients with differentiated thyroid carcinoma (DTC) who received high-dose I-131 ablation therapy after total thyroidectomy. Methods. We analyzed 218 consecutively enrolled patients who were diagnosed with DTC and underwent total thyroidectomy. All patients underwent I-131 ablation at. doses of 100-200 mCi, and. stimulated serum Tg was measured ai the time of I-131 ablation therapy. To assess disease-free status after I-131 ablation therapy, stimulated serum Tg levels, diagnostic whole-body scan (DxWBS) and. neck ultrasonography (US) were performed 6-12 months after I-131 ablation. Results. The relevant cutoff value of postoperative stimulated Tg for the prediction of disease-free status was 2 ng/mL. A total of 138 patients (63.3%) showed values of <2 ng/mL. Postoperative-stimulated Tg < 2 ng/mL had a negative piedictive value of 94.9%, which increased to 97.7% when low Tg was combined with negative neck US findings. Conclusion. Postoperative-stimulated Tg at the time of I-131 remnant ablation is a useful biochemical marker for the prediction of disease status in patients with DTC. When high-dose I-131 remnant ablation is performed after total thyroidectOmy, the stimulated Tg measurement and DxWBS that are usually performed 6-12 months after I-131 ablation therapy may be skipped, at least in low- and intermediate-risk patients with postoperative stimulated Tg of < 2 ng/mL and negative neck US findings.