Early post-treatment risk stratification of differentiated thyroid cancer: comparison of three high-sensitive Tg assays.

OBJECTIVE: To assess the diagnostic performance of three high-sensitive assays in a cohort of TgAb-negative and TgAb-positive differentiated thyroid cancer (DTC) patients.

DESIGN: Retrospective study on prospectively selected DTC patients.

METHODS: Serum samples from 154 DTC patients were obtained 6-12 months after radioiodine ablation and tested by Beckman, Roche, BRAHMS Tg and TgAb assays, respectively. Receiver operating characteristics curves for Tg were plotted using outcome over time as benchmark and assay-specific Tg thresholds were obtained for TgAb-negative and TgAb-positive patients.

RESULTS: The frequency of positive TgAb was 21, 20 and 20% for Beckman, Roche and BRAHMS, respectively. In TgAb-negative patients, clinical sensitivities and specificities of 100% and 85-95%, respectively, were observed across all assays. In TgAb-positive patients, clinical sensitivities and specificities of 80-100% and 92-96%, respectively, were observed using lower thresholds than in patients without TgAb.

CONCLUSIONS: Adopting appropriate thresholds, lower than those for TgAb-negative patients, is possible to reliably follow TgAb-positive patients using highly sensitive Tg assays.