The role of a new polyclonal competitive thyroglobulin assay in the follow-up of patients with differentiated thyroid ca
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ORIGINAL ARTICLE
The role of a new polyclonal competitive thyroglobulin assay in the follow-up of patients with differentiated thyroid cancer with structural disease but low levels of serum thyroglobulin by immunometric and LC-MS/MS methods Leila Guastapaglia1 Teresa S. Kasamatsu1 Claudia Cristina D. Nakabashi1,2 Cléber P. Camacho1,3 Rui M. B. Maciel1,2 José Gilberto H. Vieira1,2 Rosa Paula M. Biscolla 1,2 ●
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Received: 26 March 2020 / Accepted: 13 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Purpose The aims of this study were to assess the role of an in-house competitive thyroglobulin assay (Tg-c) in the followup of metastatic differentiated thyroid carcinoma (DTC) patients who presented underestimated Tg measurements by immunometric assays (Tg-IMA) and to compare the results with IMA and LC-MS/MS Tg methods. Methods This prospective study included 40 patients. Twenty-one with metastatic disease: 14 had Tg-IMA levels inappropriately low or undetectable (eight patients with positive and six with borderline TgAb) and seven had high Tg-IMA levels. Nineteen had an excellent response to therapy. The competitive assay employs a polyclonal antibody produced in rabbits immunized with human Tg, Tg labeled with biotin, and for the solid phase separation, a monoclonal anti-rabbit IgG antibody adsorbed to microtiter plates. Results All 14 patients with structural disease and underestimated levels of Tg-IMA presented detectable Tg-c levels. The median Tg-c level in the group with positive TgAb was 183 µg/L (range: 22–710 µg/L), and 58 µg/L (range 23–148 µg/L) in the borderline TgAb group. The levels of Tg-LC-MS/MS were detectable in some patients (range < 0.5–18 µg/L). All seven patients with high Tg-IMA presented also high levels of Tg-c. Only 2/19 patients with excellent response had Tg-c levels above the functional sensitivity. Conclusions The competitive assay was able to detect Tg in all patients, even in the presence of serum TgAb, and may be an option in patients with underestimated Tg-IMA and relevant structural disease. Keywords Thyroglobulin LC-MS/MS Competitive assay Thyroglobulin antibodies and thyroid cancer ●
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Introduction Serum thyroglobulin (Tg) is the main biochemical marker and an independent predictor of disease persistence and
* Rosa Paula M. Biscolla [email protected] 1
Thyroid Diseases Center and Laboratory of Molecular and Translational Endocrinology, Division of Endocrinology, Department of Medicine, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
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Fleury Medicina e Saúde, São Paulo, Brazil
3
Molecular Innovation and Biotechnology Laboratory, Medical Postgraduation Division, Universidade Nove de Julho (Uninove), São Paulo, Brazil
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recurrence in differentiated thyroid carcinoma (DTC) patients. After treatment with total thyroidectomy and radioiodine ablation, undetectable Tg measured under TSH suppression by immunometric assays (Tg-IMA) with functional sensit
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