Serum Thyroglobulin: Preoperative Levels and Factors Affecting Postoperative Optimal Timing following Total Thyroidectomy

OBJECTIVE: We evaluated if preoperative TG levels affected postoperative levels and if other factors may influence the optimal time to check postoperative TG. METHODS: This is a prospective, observational pilot study. We approved and enrolled 50 subjects ≥ 19 years scheduled for total thyroidectomy and measured serum TG, thyroglobulin antibody (TG ab), and TSH preoperatively and post thyroidectomy at 7-14 days, 4 and 6 weeks, and 3 months in subjects with benign pathology, with additional 6- and 12-month measurements in subjects with thyroid cancer. RESULTS: Preoperative TG was significantly higher in the benign (median 167.5 ng/mL vs 30.8 ng/mL) than in the malignant (p = 0.0006) group. In the benign group, 76.5% (13/17) of subjects had an undetectable TG < 0.2 ng/mL by 12 weeks postoperatively. In the malignant group, 70.6% (12/17) of those who did not receive RAI therapy and 25% (1/4) of those who did receive RAI had undetectable TG < 0.2 ng/mL by 12 weeks. Subset analysis showed 94.1% (16/17) of the benign, 70.6% of the malignant without RAI, and 50% (2/4) of the malignant with RAI achieved TG < 1.0 ng/mL by 6 weeks postoperatively. Four subjects in the malignant group reached undetectable TG levels as early as 7-14 days postoperatively. CONCLUSION: Preoperative TG levels did not predict the risk of malignancy nor time to TG nadir postoperatively. We did not find a difference in TG elimination half-life between the benign and malignant groups. The median time to reach undetectable TG levels in both benign and malignant groups who did not receive RAI therapy was 12 weeks. However, those with preexisting hypothyroidism and hyperthyroidism had lower levels of TG overall in the malignant group which can be taken into consideration besides other known factors that can affect TG levels post thyroidectomy. This trial is registered with Clinicaltrials.gov NCT02347683.