Revista Portuguesa de Endocrinologia, Diabetes e Metabolismo - Online first: 2018-06-05
Measurement of anti-thyroglobulin antibodies, a matter of method?
Introduction: The presence of anti-thyroglobulin antibodies (ATG) can induce falsely lower thyroglobulin (TG) values, which interferes in patient's follow-up with differentiated thyroid carcinoma (DTC). There are a few available methods/equipment for ATG measurement with different characteristics and great variability of results. Objective: To evaluate the qualitative variability of ATG results (positive/negative) obtained by five different immunoassays, used in Portugal. Methods: A cross-sectional retrospective study was conducted in February-March of 2016. Patients followed at Instituto Português de Oncologia de Lisboa Francisco Gentil, with negative ATG by Unicap, were selected and 3 groups constituted: (A) patients with DTC, total thyroidectomy, TG<0,2 ng/mL; (B) patients without DTC and positive anti-thyroidperoxidase antibodies (TPO); (C) individuals without DTC and negative TPO. ATGs were measured by Architect®, Immulite®, Cobas® and Advia® and classified based on the cut-off of each manufacturer. Results: A total of 141 samples were analyzed. ATG were negative by all methods in 86 (61%) samples. The number of positive results, obtained by the different equipment, showed statistically significant differences between all groups, which were more relevant in Group B. Discussion: ATG results are equipment dependent and consequently can influence the follow-up strategy of patients with DTC. This work reinforces the need of using the same method during patients follow-up.