RESUMO
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.
