Objective To investigate the predictive effect of thyroglobulin antibody (TgAb) level after operation and the trend of TgAb change after ¹³¹I treatment on the curative effect of ¹³¹I treatment in patients with differentiated thyroid carcinoma (DTC).

Methods A total of 95 patients with DTC who were positive for TgAb and who underwent total thyroidectomy and ¹³¹I treatment in the Tongji Hospital of Tongji Medical College of Huazhong University of Science and Technology from December 2016 to May 2018 were retrospectively analyzed. The patients included 16 males and 79 females, aged 11−63 (37.74±11.27) years old. ¹³¹I treatment was administered 2–6 months after surgery. Based on the response to therapy assessment system of DTC in the American Thyroid Association Management Guidelines and according to the images, the curative effect was divided into three groups, namely, structural excellent response group (A group, 54 cases), structural incomplete response group (B group, 19 cases), and structural indeterminate response group (C group, 22 cases). The following parameters were observed among the three groups: TgAb level before ¹³¹I treatment; percentage change at 1.5 months, 3–6 months, and 6–12 months; and rate of change of TgAb. The factors that might affect the curative effect were analyzed. Receiver operating characteristic (ROC) curves were drawn with the following: the TgAb level before ¹³¹I treatment; percentage change of TgAb at 1.5 months after treatment; and percentage change of TgAb at 3–6 months after treatment. The best critical value for predicting therapeutic effect was determined, and the diagnostic efficiency was calculated. The measurement data were compared through variance analysis or Kruskal-Wallis rank sum test. Chi-square test or Fisher's exact text were used to compare the count data among the groups. The multivariate Logistic regression analysis was used to analyze the factors that may affect the curative effect.

Results The univariate regression analysis results showed that the mean age (F=3.48, P=0.03), lymph node metastasis rate (χ²=10.28, P<0.01), TgAb level before ¹³¹I treatment (χ²=16.03, P<0.01), ¹³¹I dose (Fisher's exact text, P=0.002), percentage changeand and rate of change of TgAb (except percentage change at 6−12 months) at 1.5 months, 3−6 months, and 6−12 months were significantly different among the three groups (χ²=8.55–22.79, all P<0.05). The multivariate Logistic regression analysis result showed that TgAb levels before ¹³¹I treatment were significantly different among the three groups (β=−0.006, OR=0.994; P<0.01), percentage change of TgAb at 1.5 months (β=0.327, OR=1.387; P=0.046), and percentage change of TgAb at 3−6 months (β=2.521, OR=12.439; P=0.041) had statistical significance. The optimal cut-off value of TgAb level on ROC curve was 201.4 U/mL with a sensitivity of 74.1% and specificity of 68.3%. The area under ROC curve (AUC) was 0.740. The optimal cut-off values of the percentage change of TgAb in 1.5 months and for 3–6 months after treatment were 9.7% and 19.2%; the sensitivities were 72.2% and 61.0%; the specificities were 87.0% and 58.5%; and the AUCs were 0.660 and 0.752, respectively.

Conclusions Postoperative TgAb level enabled the prediction of the therapeutic effect of ¹³¹I. Patients with lower TgAb level showed better therapeutic effect. The decrease of TgAb after treatment was more significant than before treatment, suggesting that the ¹³¹I therapeutic effect was satisfactory.