Abstract: Background and purpose: It was controversial that value of the first pre-ablation stimulated thyroglobulin (sTg) in the diagnosis of recurrence or metastasis of differentiated thyroid carcinoma (DTC), due to the influence of many factors such as residual thyroid. In this study, we investigated the significance of the first pre-ablation sTg in predicting neck and distant metastasis in postoperative patients with DTC. Methods: The study included 106 patients with DTC who had undergone total thyroidectomy and lymphadenectomy. The pre-ablation sTg of 106 patients was measured one day before the first ¹³¹I ablation therapy, and the patients underwent ¹³¹I whole-body imaging and SPECT/CT fusion imaging 5-7 days after ¹³¹I ablation therapy. Patients were divided into 3 groups as M0 group, M1 group and M2 group according to the presence and absence of metastases, respectively. The sTg values between groups were compared by Mann-Whitney rank-sum test. The ROC curves and diagnostic critical point (DCP) were analyzed to evaluate the predictive value of sTg. Results: The pre-ablation sTg of M1 group and M2 group were significantly higher than that of M0 group (U=143.00, P<0.01; U=60.00, P<0.01). Areas under the ROC curve for sTg were 0.872 and 0.964, respectively. The cut-off values of DCP of sTg were 23.95 ng/mL with a sensitivity of 68.42%, specificity of 100%, accuracy of 92.31%, and 20.93 ng/mL with a sensitivity of 85.71%, specificity of 100%, accuracy of 95.40%, respectively. Conclusion: The pre-ablation sTg value may be a useful diagnostic marker for predicting metastasis before the first ¹³¹I ablation therapy, especially for the prediction of distant metastasis.

Key words: Differentiated thyroid carcinoma, Thyroglobulin, Radioiodine therapy