Lymph Node Metastases of Differentiated Thyroid Carcinoma: Does Serum Anti-Tg Antibodies or TSH Level Influence Tg measurement in Fine Needle Aspiration Washouts?

Abstract Introduction: Thyroglobulin evaluation in the washout of fine-needle aspiration (FNA-Tg) is an accurate diagnostic method of lymph node metastases (LNM) of differentiated thyroid carcinoma (DTC). Serum anti-thyroglobulin antibodies (AATg) may cause falsely low serum Tg values, but their effect on FNA-Tg has not been well established. There are also concerns about the possibility that suppressed TSH results in false-negative FNA-Tg. Our objectives were to evaluate the effect of serum AATg and TSH level on FNA-Tg of LNM of DTC and to determine the presence of AATg on the washout of fine needle aspiration (FNA-AATg). Methods: Retrospective analysis of patients who underwent FNA-Tg assay in LNM of DTC. The sample was divided in two groups according to the presence of serum AATg at the time of FNA-Tg evaluation (Group 1: positive AATg, n =47; Group 2: negative AATg, n =50). Results: There was no significant difference in the FNA-Tg between the two groups ( p =0.066), although it was lower in Group 1 (1428 ng/mL) than in Group 2 (14842 ng/mL). FNA-Tg was able to identify 10.3% LNM of DTC that would not be diagnosed based solely on cytology. FNA-AATg evaluation was positive in 12.8% of the Group 1 patients and did not seem to interfere with FNA-Tg value ( p =0.732). There were no differences in the median FNA-Tg measurements between those on levothyroxine suppressive therapy and those on substitutive therapy ( p =0.800). Conclusion: FNA-Tg assay appears to be a good diagnostic tool even in patients with positive serum AATg and those under suppressive levothyroxine therapy.