Endocrine Abstracts

Surgery followed by ¹³¹I ablative therapy (IAT) is the usual treatment for patients with differentiated thyroid carcinoma (DTC). Thyroglobulin levels obtained 9–12 months after IAT under TSH stimulation (Tg2) is a very reliable marker for the presence of thyroid tissue. The value of stimulated thyroglobulin previous to ablation (Tg1) is more controversial. The aim of this study was to examine the relationship between Tg1 and Tg2.

Material and methods: Seventy-five patients treated for a DTC between 2001 and 2006 were studied. All patients had undergone total o near-total thyroidectomy followed by IAT after thyroid hormone withdrawl or stimulation with Thyrogen. Serum TSH, Tg and Tg antibodies (Tg Ab) were measured postoperatively just before IAT or three days after the second dose of Thyrogen and 9-12 months after ablation with stimulation of TSH. Serum Tg was measured by inmunoradiometric assay with functional sensitivity of 0.5 ng/ml.

Results: Twenty-four patients were excluded: 1 with evidence of macroscopic disease, 5 with TgAb positive, 8 patients in which TgAb were not measured and 10 who had not Tg2 done. The remaining 51 were divided in three groups as follows: Group 1 (n=11) Tg1 between 0 and 1 ng/ml: all of them had Tg2 <1 ng/ml; Group 2 (n=21) Tg1 between 1 and 5 ng/ml: 2 presented Tg2 >1 ng/ml; Group 3 (n=19) Tg1 >5 ng/ml: 6 with Tg2 >1 ng/ml. ¹³¹I uptake outside the thyroid bed was demonstrated in 3 patients in group 1, 5 in group 2 and 10 in group 3.

Discussion: The prognostic value of the Tg levels measured just before IAT is often debated because of the presence of thyroid remnants that contribute to the Tg synthesis. In our series, patients with Tg levels <2 ng/ml before IAT did not show Tg >1 ng/ml 9–12 months post ablation.