Objective: A retrospective study to assess the relationship between stimulated Tg (sTg) levels before RAI therapy and response to RAI in patients with DTC who underwent thyroidectomy. Also, to evaluate sTg before RAI impact on DFS (disease-free survival).

Patients and Methods: Fifty patients with DTC treated with RAI ablation after total thyroidectomy were involved in our retrospective study between January 2015 and April 2020.

Results: Most of our patients were females 43 (75.4%). Almost 91.2% of patients were papillary thyroid carcinoma (PTC). Forty-four (77.2%) patients were early-stage T1,2, while 13 patients (22.9%) were T3,4. The post ablation Tg was <1ng/ml in 52.6%, from 1-10ng/ml in 36.8%, and >10ng/ml in 10.5% of patients. The univariate and multivariate analyses show disease stage and RAI dose as the most independent prognostic factors of DFS. The age, gender, histopathological type, T-stage, nodal status, and TG level were all without statistical significance. However, pairwise Fisher's exact tests (2X2) revealed no statistically significant difference between all pairs (P = 0.303 comparing intermediate vs. both excellent and incomplete). Also, there was a marginally significant difference in Baseline stimulated TG between the three responses (P=0.053). However, most excellent has a low level while most incomplete has a high level (P =0.025). Comparing the level in excellent vs. intermediate (P=0.145) and between intermediate vs. incomplete (P=422) showed no statistical statistically significant difference.

Conclusion: The sTg level is associated with risk stratification in patients with DTC. sTg serves as a predictor of response to initial treatment, recurrence, and metastasis.