Undetectable Sensitive Serum Thyroglobulin (<0.1 ng/ml) in 163 Patients with Follicular Cell-Derived Thyroid Cancer: Results of rhTSH Stimulation and Neck Ultrasonography and Long-Term Biochemical and Clinical Follow-Up

Context: Surveillance of patients with differentiated thyroid cancer (DTC) is achieved using serum thyroglobulin (Tg), neck ultrasonography (US), and recombinant human TSH(rhTSH)-stimulated Tg (Tg-stim). Objective: Our primary aim was to assess the utility of rhTSH Tg-stim in patients with suppressed Tg (Tg-supp) below 0.1 ng/ml using a sensitive assay. Our secondary aims were to assess the utility of US and to summarize the profile of subsequent Tg-supp measures. Design: This is a retrospective study conducted at two sites of an academic institution. Patients: A total of 163 patients status after thyroidectomy and radioactive iodine treatment who had Tg-supp below 0.1 ng/ml and rhTSH Tg-stim within 60 d of each other were included. Results: After rhTSH stimulation, Tg remained below 0.1 ng/ml in 94 (58%) and increased to 0.1-0.5 in 56 (34%), more than 0.5-2.0 in nine (6%), and above 2.0 ng/ml in four (2%) patients. Serial Tg-supp levels were obtained in 138 patients followed over a median of 3.6 yr. Neck US were performed on 153 patients; suspicious exams had fine-needle aspiration (FNA). All positive FNA were identified around the time of the initial rhTSH test. Six of seven recurrences were detected by US (Tg-stim > 2.0 ng/ml in one, 0.8 in one and <= 0.5 in four). One stage IV patient had undetectable Tg-stim. Conclusion: In patients with DTC whose T-4-suppressed serum Tg is below 0.1 ng/ml, long-term monitoring with annual Tg-supp and periodic neck US are adequate to detect recurrences. In our experience, rhTSH testing does not change management and is not needed in this group of patients. (J Clin Endocrinol Metab 97: 2714-2723, 2012)