Context. One year after initial treatment, low-risk differentiated thyroid cancer (DTC) patients undergo rhTSH-stimulated serum Tg (rhTSH-Tg) and neck-ultrasound (US).

Objective. The need for further rhTSH-Tg in these patients is controversial. We evaluated the utility of a second rhTSH-Tg in DTC patients 2–3 years after their first evaluation.

Results. At the first rhTSH-Tg, basal and stimulated serum Tg was undetectable in 68/85 patients. Neck US was unremarkable in all but one, who had evidence of lymph node disease. Seventeen/85 patients had undetectable serum Tg that became positive after rhTSH, with negative imaging in 10 and evidence of disease in 7.

Patients with no evidence of disease were reevaluated 2–3 years later (2^nd rhTSH-Tg). In patients in which the 1^st stimulated-Tg was undetectable, all had undetectable basal serum Tg, which remained undetectable after rhTSH in 66/67 patients (98.5%) and became detectable in 1 (1.5%) (positive neck-US). In the 10 patients with detectable stimulated-Tg in the 1^st test, basal serum Tg and US were negative at the 2^nd test, but rhTSH-Tg became detectable in 6. Compared to the 1^st rhTSH-Tg, the 2^nd stimulated-Tg in these 6 patients decreased in 1, increased in 3 and stabilized in 2 patients.

Conclusions. The second rhTSH-Tg was informative in patients who had 1^st stimulated-Tg detectable but not in those who had undetectable Tg at the 1^st test, in which the only patient with recurrence was diagnosed by neck-US. Thus, rhTSH-Tg should be repeated only in patients who have had a positive first rhTSH-Tg and negative imaging.