Importance of Postoperative Stimulated Thyroglobulin Level at the Time of 131I Ablation Therapy for Differentiated Thyroid Cancer

Background: Serum thyroglobulin detection plays an essential role during the follow-up of thyroid cancerpatients treated with total/near total thyroidectomy and radioiodine ablation. The aim of this retrospective studywas to evaluate the relationship between stimulated serum thyroglobulin (Tg) level at the time of high dose 131Iablation and risk of recurrence, using a three-level classification in patients with differentiated thyroid cancer(DTC) according to the ATA guidelines. Also we investigated the relationship between postoperative stimulatedTg at the time of ablation and DxWBS results at 8-10 months thereafter. Materials and
Methods: Patientswith radioiodine accumulation were regarded as scan positive (scan+). If there was no relevant pathologicalradioiodine accumulation or minimal local accumulation in the thyroid bed region, this were regarded as scannegative (scan-) at the time of DxWBS. We classified patients in 3 groups as low, intermediate and high riskgroup for assessment of risk of recurrence according to the revised ATA guidelines. Also, we divided patients into3 groups based on the stimulated serum Tg levels at the time of 131I ablation therapy. Groups 1-3 consisted ofpatients who had Tg levels of ≤2 ng/ml, 2-10 ng/ml, and ≥10 ng/ml, respectively.
Results: A total of 221 consecutivepatients were included. In the high risk group according to the ATA guideline, while 45.5% of demonstratedScan(+) Tg(+), 27.3% of patients demonstrated Scan(-) Tg(-); in the intermediate group, the figures were 2.3%and 90.0% while in the low risk group, they were 0.6% and 96.4%. In 9 of 11 patients with metastases (81.8%),stimulated serum Tg level at the time of radioiodine ablation therapy was over 10, however in 1 patient (9.1%)it was <2ng/mL and in one patient it was 2-10ng/mL (p=0.005). Aggressive subtypes of DTC were found in 8 of221 patients and serum Tg levels were ≤2ng/ml in 4 of these 8.
Conclusions: We conclude that TSH-stimulatedserum thyroglobulin level at the time of ablation may not determine risk of recurrence. Therefore, DxWBSshould be performed at 8-12 months after ablation therapy.