Consideration of Serum Thyrotropin When Interpreting Serum Thyroglobulin Level in Patients with Differentiated Thyroid Cancer

Abstract

Background and Objectives: The level of thyroid-stimulating hormone (TSH)-stimulated thyroglobulin (Tg) after thyroid hormone withdrawal (THW) is the most sensitive marker for detecting recurrence of differentiated thyroid cancer (DTC). In DTC, Tg production is regulated by TSH; however, TSH values after THW are never identical, even in the same patient. The objective of this study was to evaluate the influence of TSH on Tg levels after THW. Materials and Methods: TSH and Tg concentrations were measured twice at 2 and 3 weeks after THW in 309 patients with DTC. TSH and Tg levels at these time points were compared. The percent change in TSH (ΔTSH) and change in Tg level (%ΔTg) from 2 to 3 weeks after THW were calculated, and Pearson's correlation coefficients were calculated to determine whether ΔTSH could affect %ΔTg. Tg cutoff value for diagnostic imaging was 2 ng/mL. Results: The TSH and Tg values at 3 weeks were significantly higher than those at 2 weeks after THW. Tg values increased significantly to ＞2 ng/mL after 1 week in 38.5% of the patients with Tg values of 0.2-2 ng/mL at 2 weeks after THW. In patients with Tg values ≥2 ng/mL at 2 weeks after THW, Tg values increased significantly after an additional week of THW. ΔTSH correlated significantly with %ΔTg. Conclusion: TSH values differed according to time after THW, and Tg values differed significantly according to TSH values. Therefore, TSH values should be considered carefully when interpreting the meaning of Tg levels in patients with DTC.