A Case of Hashimoto's Thyroiditis with Markedly Elevated Serum Thyroglobulin and Evidence of its Influence on the Measurement of Anti-Thyroglobulin Antibody by Highly Sensitive Assays

Abstract. We present the case of a 66-year-old woman with Hashimoto's thyroiditis, who showed extremely high concentrations of serum thyroglobulin（Tg）. Serum Tg levels were markedly elevated following a slight elevation of serum thyrotropin（TSH）（22,000 ng/mL and 11.1 μU/mL, respectively）. Although elevated concentrations of serum Tg declined concomitant with decrease of serum TSH one month later, Tg concentrations remained high （＞948 ng/mL）even at normal or suppressed TSH levels. There was no evidence of massive thyroid tissue damage or thyroid tumor. To our knowledge, there have been no case reports of such high concentrations of serum Tg （＞2×104 ng/mL）in the clinical course of Hashimoto's thyroiditis. Furthermore, we showed evidence that extremely high Tg levels could possibly influence the measurement of anti-Tg autoantibody using highly sensitive radioimmunoassays.