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®. ATGs 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.
|Positive ATG||Q test|
|(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.
20 May 2017 - 23 May 2017