Clinical implications of changing thyroglobulin and antithyroglobulin antibodies analytical methods in the follow-up of patients with differentiated thyroid carcinoma

•Elecsys and Access immunoassays show a proportional and systematic bias for Tg quantification.•They classify similarly the response of patients with differentiated thyroid cancer.•Good agreement in patients response classification, avoids the need for Tg confirmation in most samples.•Ab-Tg had a hi...

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Published in:	Clinica chimica acta Vol. 548; p. 117502
Main Authors:	Deza, Sara, Maroto, Julia, Tellechea, Olaia, Orbegozo, Natalia, Merino, Juana, Galofré, Juan C, Alegre, Estibaliz, González, Álvaro
Format:	Journal Article
Language:	English
Published:	Netherlands Elsevier B.V 01-08-2023
Subjects:	Anti-thyroglobulin antibodies Differentiated thyroid cancer Immunoassay Method comparison Thyroglobulin Immunoassay DTC Tg Thyroglobulin CI Anti-thyroglobulin antibodies Method comparison Differentiated thyroid cancer Ab-Tg ATA
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Summary:	•Elecsys and Access immunoassays show a proportional and systematic bias for Tg quantification.•They classify similarly the response of patients with differentiated thyroid cancer.•Good agreement in patients response classification, avoids the need for Tg confirmation in most samples.•Ab-Tg had a higher bias and lower agreement between those methods than Tg assays.•This minor agreement for Ab-Tg does not invalidate the good agreement in patients response classification. Patients’ response to treatment in differentiated thyroid cancer (DTC) is classified according to serum thyroglobulin concentrations (Tg), usually using the American Thyroid Association guidelines and considering potential interfering anti-thyroglobulin antibodies (Ab-Tg). We aim to evaluate the clinical implications of changing Tg and Ab-Tg quantification method. Tg and Ab-Tg were quantified in 82 serum samples (60 from DTC patients) by Elecsys and Access immunoassays. Elecsys immunoassay rendered higher values of Tg than Access: mean bias 5.03 ng/mL (95%CI:-14.14–24.21). In DTC patients, there was an almost perfect agreement for response classification (kappa index = 0.833). Discrepancies appeared in patients with undetermined response, with a more tendency to subclassification with Access. Ab-Tg showed a poor correlation (r = 0.5394). When Elecsys cut-off was reduced to 43 IU/mL, agreement for positive/negative classification improved from a kappa index of 0.607 to 0.650. Prospective study with personalized follow-up showed that only 6.3% of Tg results required an analytical confirmation, being confirmed 93% of them. Despite the biases observed, clinical impact of an analytical change is minimal in patients’ management. However, cautious and personalized follow-up period after the change is still mandatory, especially in patients with Tg levels between 0.2 and 1 ng/mL.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0009-8981 1873-3492
DOI:	10.1016/j.cca.2023.117502