ObjectiveTo evaluate the diagnostic values of TgAb levels, the median time for disappearance, and the change trend of TgAb after 131I radiotherapy in Tg-negative patients with DTC.Methods116 DTC patients who had undergone thyroidectomy in the case of Tg-negative and TgAb-positive from July 2012 to November 2016 were enrolled in this retrospective study.The patients were divided into two groups as M1(n=44) and M0(n=72) according to with or without metastasis /recurrence.We compared TgAb levels between the two groups by independent-sample t test.We used survival analysis to assess the median time for disappearance of TgAb of the patients who were followed for 6 to 29 months and followed up these patients’ states and course of disease corresponding to the change trend of TgAb levels dynamically after 131I radiotherapy.ResultsBoth the values of TgAb (t=0.221,P=0.825) and the median time for disappearance of TgAb (P=0.567) between M1 group and M0 group were not significantly different.During the follow-up period, among patients whose TgAb were gradually decreased or became negative there were 96.8% (61/63) patients who were cured or improved, while whose TgAb were gradually increased or remained persistently high there were 31% (9/29) patients who were ineffective or became worse.ConclusionsValue of TgAb and the median time for disappearance of TgAb cannot predict recurrence or metastasis of DTC in the case of Tg-negative, but the change pattern of TgAb levels is of vital importance to the treatment effect and prognosis of disease.