Endocrine Abstracts

Objectives: Thyroglobulin (Tg) play an important role in managements of well-differentiated thyroid carcinoma (DTC). Undetectable TSH-stimulated serum Tg level in the absence of antithyroglobulin antibody (AbTg) indicates complete remission. Circulating AbTg may interfere with Tg assay and may cause false negative results. Moreover, undetectable Tg is observed in a part of patients after total thyroidectomy(TT), even if serum AbTg concentration is low.

The aim of our study was to evaluate a clinical significance of Tg and AbTg levels measured before and 6-12 month after thyroid ablation.

Materials and methods.: 329 patients after TT because of DTC were treated with radioiodine(RIT). Diagnostic procedures - including whole-body scan (WBS) and measurements of Tg and AbTg levels were performed before and 6–12 month after 131I administration. Finally, we analyzed the subgroup of 104 patients, who had: 1) no evidence of distant metastases, 2) undetectable Tg (<1ng/ml) and/or elevated level of AbTg (>60U/ml) before RIT 3) complete data for study variables.

Results.: Among the 329 patients, 143 (43.5%) had elevated (↑) Tg and normal (n) AbTg level, 32 (9.7%) - Tg(↑) and AbTg(↑), 109 (33.1%) - Tg(n) and AbTg(n), 45 (13.7%) - Tg(n) and AbTg(↑)

Our group of 104 patients included

16 patients - Tg(↑) and AbTg(↑)

66 patients - Tg(n) and AbTg(n)

22 patients - Tg(n) and AbTg(↑)

6–12 months after 131I therapy, all these patients had undetectable Tg level. Among 38 patients with AbTg(↑) previously, 21 (55.3%) had AbTg (n)- subgroup A, 9 (23.7%) - AbTg decreased, but were still elevated- subgroup B, 5 (13.2%) - AbTg on the same level - subgroup C and 3 (7.9%) - AbTg increased - subgroup D. Diagnostic WBC was positive (persistent thyroid bed uptake) in 11/38 patients: 6 in A, 3 in B, 1 in C and 1 in subgroup D.

In the rest of 66 patients /(Tg(↑) and AbTg(↑) WBS was positive in 6.

Conclusions: In more than 50% of patients with DTC serum Tg concentration could not be used as an indicator of the effectiveness of thyroid ablation - because of coexistence of AbTg or/and undetectable level of Tg before treatment. WBS provides more important information and should be routinely used in early follow-up of patients after thyroid ablation.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector