Measurement of anti-thyroglobulin antibodies, a matter of equipment?

Ricardo Capitao; Susana Prazeres; Ana Font; Conceicao Godinho; Isaura Rodrigues; Frederico Cerveira; Graca Belo; Joao Viana; Deolinda Madureira

doi:10.1530/endoabs.49.EP1330

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Endocrine Abstracts (2017) 49 EP1330 | DOI: 10.1530/endoabs.49.EP1330

ECE2017 Eposter Presentations: Thyroid Thyroid (non-cancer) (260 abstracts)

Measurement of anti-thyroglobulin antibodies, a matter of equipment?

Ricardo Capitão ¹ , Susana Prazeres ² , Ana Font ² , Conceição Godinho ³ , Isaura Rodrigues ³ , Frederico Cerveira ⁴ , Graça Belo ¹ , João Viana ¹ & Deolinda Madureira ⁵

Author affiliations

¹Hospital Egas MonizCentro Hospitalar Lisboa Ocidental, Lisboa, Portugal; ²Instituto Português de Oncologia de Lisboa Francisco Gentil, Lisboa, Portugal; ³Centro Hospitalar Lisboa Central, Lisboa, Portugal; ⁴Centro Hospitalar do Baixo Vouga, Aveiro, Portugal; ⁵Sociedade Portuguesa de Endocrinologia Diabetes e Metabolismo, Lisboa, Portugal.

Introduction: The presence of anti-thyroglobulin antibodies (ATG) can induce falsely lower thyroglobulin (Tg) values. The methods characteristics used for ATG measurement vary according to the equipment/reagent used. ATG at our centre is measured by Unicap.

Objective: To assess if patients with negative ATG by Unicap^® have different results with other equipment.

Methods: A cross-sectional retrospective study was conducted in February-March of 2016, in which blood samples from patients followed at our Centre, with negative ATG, were selected and separated into three groups: 1) differentiated thyroid carcinoma (DTC), total thyroidectomy, Tg<0.2 ng/ml; 2) without DTC and positive TPO; 3) without DTC and negative TPO. ATGs were measured by Immulite^®, Cobas^®, Architect^® and Advia^®. ATG’s classification was based on the cut-off of each manufacturer. Q-Chrocan test was used to calculate the p-values (P<0.05 were considered statistically significant).

Results: A total of 141 samples were analysed. The results are described in the table below: high significant differences were found between the various methods in all groups. The Architect and the Immulite had the highest and lowest rate of ATG positives, respectively, compared to Unicap.

**Table 1**
		Positive ATG					Q test
Group	N	Unicap	Immulite	Cobas	Architect	Advia	χ²	P
(A) DTC+/Tg<0.2	88	0	1 (1%)	3 (3%)	23 (26%)	6 (7%)	70.0	<0.001
(B) DTC−/TPO+	28	0	2 (7%)	8 (29%)	26 (93%)	11 (39%)	67.2	<0.001
(C) DTC−/TPO−	25	0	0	1 (4%)	6 (24%)	2 (8%)	17.7	0.001
Total	141	0	3 (2%)	12 (9%)	55 (39%)	19 (14%)	152.7	<0.001

Discussion: ATG results depend on the equipment used. This can influence the follow-up strategy of patients with DTC. These results also raise the question of which method is more reliable for ATG detection and how a result of ‘ATG positive’ actually influences the Tg measurement.