Adjunctive diagnostic tool for serum thyroglobulin (Tg) testing with or without radioiodine imaging in the follow up of patients with well-differentiated thyroid cancer who have previously undergone thyroidectomy. Adjunctive treatment for radioiodine ablation of thyroid tissue remnants in patients who have undergone a near-total or total thyroidectomy for well differentiated thyroid cancer and who do not have evidence of metastatic thyroid cancer.