TG and neoplasm: In patients treated with 131I, sTg is not necessary if basal Tg is significantly elevated (traditionally > 1 ng/mL) or, at the other extreme, in patients with the following criteria: (i) apparently complete tumor resection, (ii) absence of uptake outside the thyroid bed on posttherapy whole-body scanning (RxWBS), (iii) low risk of persistent or recurrent disease (PRD), (iv) neck ultrasound (US) showing no tumor, (v) absence of interference of anti-Tg antibodies (TgAb), and (vi) basal Tg “undetectable” by a second-generation assay (functional sensitivity of approximately 0.1 ng/mL).