RESUMO
OBJECTIVE: To determine the interference of antithyroglobulin (TgAb) on the measurement of serum thyroglobulin (Tg) in patients with differentiated thyroid carcinomas (DTC). METHODS: The Tg positive serum and TgAb positive serum were taken from the patients with total thyroidectomy and thyroid remnant ablation by radioiodine. The Tg positive serum contained high level of Tg (>10 microg/L) and nondetectable TgAb. The TgAb positive serum contained high level of TgAb (>115 IU/mL) and nondetectable Tg. We incubated a constant amount of Tg with increasing volumes of Tg-free autoantibodies and allowed them to equilibrate at room temperature for 12 hours before measuring Tg and TgAb. The thyroglobulin and TgAb values were determined by the Roche electrode induce chemiluminescent emission system with monoclonal antibody sandwich analysis. The correlation between TgAb and serum Tg values was analysed. RESULTS: TgAb led to underestimation of serum Tg values by 15%-50% in 8 patients with DTC. TgAb was correlated with the magnitude of underestimated serum Tg values in 3 patients with DTC, but not in the other 5 patients with DTC. CONCLUSION: TgAb underestimated serum Tg values in a dose-dependent manner in some patients with DTC, but not in others.