Is a second recombinant human thyrotropin stimulation test useful? The value of postsurgical undetectable stimulated thyroglobulin level at the time of remnant ablation on clinical outcome.

Objective The management of patients with differentiated thyroid cancer ( DTC) has changed in recent years, and monitoring depends on the risk of persistent/recurrent disease. The objective was to assess the prognostic value of a single stimulated thyroglobulin (Tg) measured at the time of the first radioiodine therapy (Stim-Tg1), and the utility of a second stimulated Tg measurement performed 6-12 months later (Stim-Tg2). We also examined the role of neck ultrasound ( US) in the early diagnosis of recurrence. Design This was a retrospective observational cohort study conducted in a tertiary referral hospital. Of 213 evaluated patients with DTC, 169 were finally included. Methods Measurement of Stim-Tg1, Stim-Tg2 and neck US. Results Stim-Tg1 was undetectable in 71 of 169 patients (42%). All of them (71/71) continued to have negative Stim-Tg2. Seventy of 71 had an excellent response to the first treatment. Sixty-eight of 71 had no evidence of disease after an average follow-up of 7·2 years. In patients with detectable Stim-Tg1 (98/169; 58%), Stim-Tg2 became negative in 40. The negative predictive value ( NPV) of Stim-Tg1 was 0·96. The optimal Stim-Tg1 cut-off level for identifying persistence was 3·65 ng/ml. Recurrence was detected in 14 patients. Neck US was useful for identifying local recurrence (13/14; 92·85%). Conclusions Stim-Tg1 is a reliable marker with a high NPV. A second stimulation test should be avoided in patients with negative Stim-Tg1. In patients with biochemical persistence, Stim-Tg2 is useful for confirming/ruling out final status. Neck US plays a valuable role in the early diagnosis of recurrence. [ABSTRACT FROM AUTHOR]