High-sensitive basal serum thyroglobulin 6-12 months after thyroid ablation is strongly associated with early response to therapy and event-free survival in patients with low-to-intermediate risk differentiated thyroid carcinomas.

OBJECTIVE: High-sensitive thyroglobulin assays (hsTg) has decreased the need for stimulated Tg measurements in patients with differentiated thyroid carcinoma (DTC). However, multiple assays analyzing the same samples may report different values. Accordingly, appropriate assay-specific cut-off levels should be selected in representative patient series. Here, we evaluate the role of a new hsTg assay in low-to-intermediate risk DTC patients and select appropriate assay-specific clinical cut-off limits.

DESIGN: This was a retrospective study. The response to treatment was assessed according to ATA.

METHODS: Patients with low-to-intermediate risk DTC treated and regularly followed-up in our thyroid center. Tg was measured on the Kryptor Compact Plus Instrument (BRAHMS Thermo Fisher Scientific).

RESULTS: The study series comprised 201 DTC patients and excellent response (ER) was demonstrated in 184 (91.5%). Optimized threshold of basal Tg (onT4-Tg) measured 6-12 months after initial treatment was set by ROC curves analysis at 0.28 ng/mL. Having onT4-Tg <0.28 ng/mL at 6-12 months after treatment was associated with longer disease-free survival of Kaplan-Meier ( P <  0.001), ER at early follow-up (odds ratio (OR): 165, P <  0.001) and absence of relapse during follow-up (OR: 328, P  = 0.0001).

CONCLUSIONS: Patients with low- and intermediate-risk DTC could be considered cured when they have onT4-Tg levels <0.28 ng/mL coupled with negative imaging at their first post-ablation visit.