Day 3 thyroglobulin ≤1 ng/ml after recombinant human TSH just prior to radioactive iodine is predictive of low risk for persistent/recurrent disease in patients with papillary thyroid carcinoma

We evaluated the negative predictive value (NPV) of thyroglobulin obtained 24 h after the second recombinant human TSH (rhTSH) ampoule (Tg-D3), before ablation with ¹³¹I, for persistent/recurrent disease (PRD) in low/intermediate risk patients with papillary thyroid carcinoma. One hundred and one patients with Tg-D3 ≤1 ng/ml without anti-Tg antibodies (TgAb) were selected. Post-therapy whole-body scanning was negative for metastases in 98 (97 %) patients, and three patients showed discrete ectopic cervical uptake, but no corresponding disease was detected by neck ultrasound or computed tomography. One year after ablation, 98 (97 %) patients were free of the disease. Three patients had stimulated Tg >1 ng/ml, but no metastases were detected by the imaging methods. During follow-up (median 50 months), tumor recurrence was observed in only one patient. Thus, the NPV of Tg-D3 ≤1 ng/ml for PRD was 99 %. Among the 101 patients with Tg-D3 ≤1 ng/ml, Tg obtained 48 h after ablation (Tg-D5) continued to be ≤1 ng/ml in 56, and 45 had Tg-D5 >1 ng/ml. None of these 45 patients had PRD. In conclusion, Tg-D3 ≤1 ng/ml had a high NPV for PRD in patients without TgAb or known persistent disease and who are not at high risk. In these patients, Tg-D5 >1 ng/ml is more likely to reflect actinic damage to the remnant thyroid tissue rather than persistence of significant normal or tumor tissue.