Optimal threshold of stimulated serum thyroglobulin level for 18 F-FDG PET/CT imaging in patients with thyroid cancer.

This study was to explore the optimal threshold of thyroid-stimulating hormone (TSH)-stimulated serum thyroglobulin (s-Tg) for patients who were to receive 18 F-fluorodeoxyglucose (18 F-FDG) PET/CT scan owing to clinical suspicion of differentiated thyroid cancer (DTC) recurrence but negative post-therapeutic 131 I whole-body scan (131 I-WBS). A total of 60 qualified patients underwent PET/CT scanning from October 2010 to July 2014. The receiver operating characteristic (ROC) curve analyses showed that s-Tg levels over 49 μg/L led to the highest diagnostic accuracy of PET/CT to detect recurrence, with a sensitivity of 89.5% and a specificity of 90.9%. Besides, bivariate correlation analysis showed positive correlation between s-Tg levels and the maximum standardized uptake values (SUVmax) of 18 F-FDG in patients with positive PET/CT scanning, suggesting a significant influence of TSH both on Tg release and uptake of 18 F-FDG. So, positive PET/CT imaging is expected when patients have negative 131 I-WBS but s-Tg levels over 49 μg/L.