Value of stimulated pre-ablation thyroglobulin as a prognostic marker in patients with differentiated thyroid carcinoma treated with radioiodine

Abstract

Objective: To determine which Thyroglobulin (Tg) level after levothyroxine (LT₄) withdrawal (stimulated thyroglobulin - sTg) measured before radioiodine therapy (RAIT) is able to predict incomplete response to treatment of differentiated thyroid carcinoma (DTC) with greater sensitivity and specificity one year after initial treatment with I¹³¹.

Methods: A chart review was performed in which 375 patients with DTC treated with RAIT were included. The sTg was measured in all patients prior to treatment with I¹³¹. Follow up were then performed one year later. Initial sTg levels were associated to DTC outcomes. A receiver operating characteristic (ROC) curve was performed to achieve a sTg level able to predict which patients would have a greater chance of having an incomplete response to RAIT.

Results: Incomplete response to treatment was found in 122 patients (32.5%), this group had a mean sTg of 23.2 ng/mL. ROC curve showed that the optimal cut-off sTg level was 4.4 ng/mL. (sensitivity: 72.1%; specificity: 72.3%; accuracy: 72.2%; positive predictive value of 55.7%; and negative predictive value: 84.3%).

Conclusion: sTg pre-ablation is a valuable predictor of DTC incomplete response to treatment one year after RAIT. Levels of 4.4 ng/ml or more showed higher accuracy to predict this outcome.

Keywords: Differentiated thyroid carcinoma; Iodine radioisotopes; Prognosis; Thyroglobulin.