Rising serum antithyroglobulin antibody levels predict recurrence of differentiated thyroid carcinoma in thyroglobulin-negative patients



SUMMARY BACKGROUND Serum antithyroglobulin antibodies (TgAbs) are found in 10 to 25% of patients with differentiated thyroid carcinoma (DTC), as compared with an incidence of approximately 10% in the general population. This poses a serious problem in the follow-up of patients with DTC, as circulating TgAb interferes with serum thyroglobulin (Tg) measurements performed by immunometric assays. Thyroid cancer management guidelines suggest that TgAb levels serve as a surrogate for serum Tg measurement during follow-up, providing TgAb is measured in the same laboratory. Kim et al. hypothesize that changes in serum TgAb might predict tumor outcome, which has been a point of contention in previous studies. The aim of this study was to determine whether a changing pattern of TgAb levels found soon after thyroidectomy could serve as a prognostic indicator. METHODS This retrospective study was performed on 1499 consecutive patients treated for DTC in the authors' hospital from 1995 through 2003. All had total thyroidectomy followed by remnant ablation with 100 to 150 mCi (3.7 to 5.55 GBq) of 131 I about 6 weeks after surgery. Patients selected for study had no preoperative evidence of extracervical tumor, or 131 I uptake outside the thyroid bed on the posttreatment whole-body scan (RxWBS) or in the thyroid bed on the first diagnostic whole-body scan (DxWBS) during follow-up. Patients with extracervical metastases or poorly differentiated or anaplastic thyroid cancer were excluded from the study. Follow-up DxWBS was performed with 4 mCi (148 MBq) of 131 I after thyroid hormone withdrawal every 3 to 6 months along with serum Tg and TgAb measurements. When serum Tg was above

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