Evaluation thyroglobulin level during suppressive therapy measured by ultrasensitive technique in the prediction of excellent response in patients with differentiated thyroid cancer

Introduction: When ultrasensitive thyroglobulin (uTg) is measured serially in the first ۱۲ months of treatment, it can probably predict recurrence of thyroid cancer without discontinuation of T۴ or administration of rhTSH. Methods: Measurement of TSH, Tg, Anti-Tg Ab, and uTg was performed in all consecutive patients with low-intermediate risk DTC ۲, ۶, and ۱۲ months after initial therapy. One year after surgery, response to therapy was evaluated. Tg and uTg levels in different time points and the trend of changes were used to predict response to therapy.Results: Overall, ۳۷ patients with a mean age of ۴۰.۳ years were studied. The mean initial uTg was significantly lower than fTg (P=۰.۰۱). Overall, the correlation coefficient was ۰.۴۵ and increased to ۰.۷۱ in ftg<۱۰ ng/ml (P=۰.۰۰۵). The majority of patients (۹۱.۹%) received a mean dose of ۳.۳± ۲.۲GBq of I-۱۳۱.  One year later, there was no significant difference in mean Tg and mean uTg between the two techniques (P=۰.۶۲). The mean offT۴uTg is not significantly different between patients with incomplete response compared to other groups at the end of the follow-up (P=۰.۱). The slope of onT۴uTg was ۰.۰۴±۰.۱۸ versus ۰.۲۴±۰.۸۲ in patients with and without incomplete response respectively (P=۰.۴۵). Using ROC analysis, onT۴uTg slope of ۰.۰۰۰۵ was the best cutoff to differentiate incomplete response from other responses, however, the sensitivity was only ۵۴.۵% and specificity was ۷۵%.Conclusion: The trend of thyroglobulin level during suppressive therapy measured by the ultrasensitive technique cannot accurately predict excellent response in DTC patients.

Keywords:

Ultrasensitive thyroglobulin assay , Thyroid cancer , Response to therapy