Prognostic Value of Serum Thyroglobulin Measured at 48 Hours Versus 72 Hours after Second Dose of Recombinant Human Thyrotropin in Surveillance of Well-Differentiated Thyroid Cancer

Objective The sensitivity of thyroglobulin (Tg) to detect differentiated thyroid cancer recurrence increases with the rise of the thyrotropin level. Since 1998, recombinant human thyrotropin (rhTSH) has been commercially available for this purpose. The traditional protocol for using rhTSH calls for 2 daily injections of rhTSH, followed by the measurement of Tg 72 hours after the second dose. In this study, we compared the performance of rhTSH-stimulated Tg (rhTSH-Tg) obtained at 48 versus 72 hours after the second rhTSH. Methods A retrospective chart review of 1088 patients with thyroid cancer was conducted. Two hundred forty-nine rhTSH-Tg, without measurable Tg antibody, were identified, 134 of which were obtained at 48 hours (4-day test) and 115 at 72 hours after the second rhTSH (5-day test). The ability of rhTSH-Tg to identify recurrence or persistence of differentiated thyroid cancer and to predict response to therapy at the end of the study period was compared between the 2 groups. Results The median duration of follow-up was 8 years. When recurrent/persistent cancer was present based on a combination of unstimulated Tg, imaging and procedures, the ratio of rhTSH-Tg ≥ 1 ng/mL was similar in both groups (P value: .153). The negative predictive value of rhTSH-Tg to predict response to therapy over the long term was 95% or higher in 4-day and 5-day tests. Conclusion Tg measured 48 and 72 hours after the second dose of rhTSH may provide a comparable prognostic value. These results encourage further studies to identify new protocols to obtain rhTSH-Tg.