Transient early increase in thyroglobulin levels post-radioiodine ablation in patients with differentiated thyroid cancer.

Objectives: Treatment of differentiated thyroid cancer (DTC) includes surgical thyroidectomy and, in most cases, radioactive iodine (RAI) ablation. Measurement of serum thyroglobulin (Tg) levels is used for assessing disease burden and identifying persistent-recurrent DTC. This prospective study determined the Tg profile before and after RAI-ablation in patients with DTC.

Design And Methods: Fifty-five DTC patients with complete resection received RAI-ablation and were assessed for Tg at baseline (non-stimulated), pre-ablation (stimulated), 7 days post-ablation (stimulated) and at 6 months (stimulated). Stimulation of Tg was achieved by thyroid hormone withdrawal to achieve serum thyroid stimulating hormone (TSH) ≥30 mU/L. Thyroid remnant size was estimated from whole body scintigraphy. Similar protocols were implemented for nine patients with incomplete resection/metastatic disease for comparison.

Results: Mean stimulated Tg levels for DTC patients with complete resection at 7 days post-RAI increased 13-fold from 13.7 to 175.5 μg/L (p<0.0001), and the Tg levels reduced to 2.3 μg/L (p<0.0001 versus post-RAI) by follow-up. None of the patients had recurrence of disease. For the nine patients with incomplete resection/metastases, Tg levels were higher throughout compared to the patients with complete resection. There was no increase in Tg between pre- and post-RAI. We did not observe a significant correlation between the remnant size and Tg increase.

Conclusions: This study confirms a prominent transient early increase in Tg post-RAI ablation in DTC patients with complete resection, with the Tg levels falling below baseline by 6 months. This is presumed to reflect RAI-induced thyroid tissue destruction/inflammation with subsequent release of Tg from the thyroid remnant. Recognizing this transient phenomenon is important for post-ablation Tg interpretation and patient management.