Abstract: Objecitve To identify the interference of endogenous antithyroglobulin (TgAb) with experimental thyroglobulin (Tg) values using dilution curves. Methods Dilution buffer, detectable TgAb serums (TgAb 20-25 IU/mL, Tg free) and undetectable TgAb serums (TgAb <10 IU/mL, Tg free) were employed to dilute the Tg serums from patients with DTC, respectively. The Tg values were detected by immunometric assay (IMA). The experimental Tg values (Y-axis) were plotted against expected serum Tg values (X-axis). Diluted curves were used to evaluate the interference of TgAb on the experimental Tg values. A linear dilution curve is supposed to appear if no TgAb interference exists. Results The Tg dilution curves with dilution buffer were linear. Thirty six dilution curves were obtained with TgAb serums from six patients diluted by detectable TgAb serums, and 12 showed linear. Tg serums from six patients diluted by one detectable TgAb serum resulted in both linear and non-linear results. One Tg serum diluted by six TgAb serums also resulted both linear and non-linear results. Tg serums from three patients diluted by five undetectable TgAb serums resulted in 11 dilution curves, four of which were linear. Conclusion Dilution curves can be used to predict TgAb interference indirectly. Detectable TgAb may not interfere with experimental Tg values. Whereas, undetectable TgAb may interfere with Tg values. TgAb could not be used to predict Tg interference. Key words Differentiated thyroid cancer Thyroglobulin