Anti-thyroglobulin antibodies (anti-Tg) interfere with the quantification of thyroglobulin (Tg) levels. Increasing levels of anti-thyroid antibodies (AT-Abs) may suggest the presence of targeted antigens (Tg and TPO) as a surrogate of differentiated thyroid follicular cells’ existence. Our aim was to assess the diagnostic efficiency of AT-Abs compared to Tg levels for determining papillary thyroid cancer (PTC) recurrence. We analyzed the records of patients treated for PTC with recurrence from 2000 to 2016 at our institution. Patients with PTC recurrence were contrasted with controls regarding Tg, anti-Tg, and anti-TPO antibodies levels at 6, 12, 24, and 36-60 months after radioiodine administration and based on the 2015 ATA response criteria stratification, as well as AT-Abs positivity status. Diagnostic efficiency measures, receiver operating characteristic curves (ROC), as well as areas under the curves (AUC), were analyzed. Fifty-one patients with PTC recurrence and 88 controls with Tg and AT-Abs determinations were identified. Groups’ comparison showed higher Tg and anti-Tg levels and a higher proportion of AT-Abs positivity in patients with recurrence. The same behavior was observed after the groups’ stratification according to the ATA 2015 dynamic response criteria. ROC analysis displayed equivalent AUC for Tg and anti-Tg after the 6 months set point. Adding anti-Tg positivity increases specificity to 97% for recurrence. Based on our results, anti-Tg negativity status must be included as an additional criterion for excellent response definition in PTC patients. Patients with anti-Tg positivity should be followed cautiously as some may develop recurrence even with currently established excellent response criteria by ATA.
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