Background: This study investigated the value of postoperative stimulated thyroglobulin (Tg) combined with neck ultrasonography for the prediction of the posttherapy whole-body scanning (RxWBS) and the efficacy of ablation with 30 mCi ¹³¹I in patients with thyroid cancer and low risk of recurrence to identify those who do not require ablation or only need a low ¹³¹I activity.

Methods: A total of 237 consecutive patients with well-differentiated thyroid cancer and low risk of recurrence who were initially treated by total thyroidectomy followed by remnant ablation with 1.1 or 3.7 GBq (30 or 100 mCi) ¹³¹I were studied. Neck ultrasonography, Tg after levothyroxine withdrawal, and anti-Tg antibodies (TgAb) were obtained before, and RxWBS was performed 7 days after ¹³¹I administration. Patients with TgAb were excluded.

Results: Postoperative ultrasonography revealed lymph node metastases in 5/237 (2%) patients. RxWBS showed ectopic uptake in 3/232 (1.3%) patients with negative ultrasonography. The negative predictive value of postoperative stimulated Tg <1 ng/mL (n = 132) or <10 ng/mL (n = 213) combined with negative ultrasonography was 100%. Among patients with detectable postoperative stimulated Tg <10 ng/mL and negative ultrasonography, 50 received 1.1 GBq ¹³¹I and 31 received 3.7 GBq. In the control assessment, stimulated Tg <1 ng/mL and neck ultrasonography without anomalies were achieved in 47/50 (94%) and in 29/31 patients (93.5%). All patients with stimulated Tg ≤1 ng/mL, negative TgAb, and normal ultrasonography before ablation continued to show the same results 8-12 months after initial therapy as expected, irrespective of the administration of 1.1 GBq (n = 82) or 3.7 GBq ¹³¹I (n = 50).

Conclusions: Measurement of stimulated Tg combined with neck ultrasonography after total thyroidectomy may exclude the need for ablation in 56% of low-risk patients without TgAb (Tg <1 ng/mL) and permit the administration of an activity of 1.1 GBq ¹³¹I in another 34% with low Tg levels.