Purpose: Recent studies have shown that thyroglobulin (Tg) concentration is a useful tumor marker in follow-up of differentiated thyroid cancer (DTC) patients after thyroidectomy and subsequent radioiodine (I-131) therapy. However, its role is controversial after total or near-total thyroidectomy before the first I-131 ablative treatment. So, we used thyroid-stimulating hormone (TSH) levels to normalize predictive values of Tg for DTC.
Methods: The study was a retrospective analysis. A total of 244 patients with DTC who had undergone a total thyroidectomy and subsequent I-131 therapy were included. Exclusion criteria were patients with high serum Tg antibody (TgAb) concentration and in whom it was not measured. Patients were divided into 2 groups as M1 and M0, according to whether the patient present with or without distant metastases.
Results: Preablative stimulated Tg in group M0 ranged between 0.1 and 348.9 ng/mL and group M1 between 0.2 and 1000 ng/mL. Tg/TSH ratios ranged 0.000667 to 12.143 ng/IU and 0.002948 to 12500 ng/IU. Both Tg and Tg/TSH values were significantly different between the 2 groups (the Wilcoxon rank sum test: Tg P < 0.0001 [z = 8.785]; Tg/TSH P < 0.0001 [z = 8.850]). The areas under receiver operating characteristic curves for Tg concentrations and Tg/TSH ratios were 0.913 and 0.916, respectively.
Conclusion: Both Tg and Tg/TSH ratios might be considered predictive markers for metastases of DTC just after total thyroidectomy before the first I-131 ablative therapy.