Multicentre clinical evaluation of the new highly sensitive Elecsys® thyroglobulin II assay in patients with differentiated thyroid carcinoma

Abstract

Objective: A highly sensitive thyroglobulin assay (Elecsys® Tg II, Roche Diagnostics, Penzberg, Germany) has become available for monitoring patients with differentiated thyroid cancer (DTC). Here, we evaluated the clinical performance of Elecsys® Tg II assay in a multicentre patients series and compare it with the established Access® Tg assay (Beckman Coulter, Brea, CA, USA). Design: Retrospective analysis on prospectively selected patients in four thyroid cancer referral centres with uniform DTC management. Participants: All DTC cases diagnosed, treated and followed up in four tertiary referral centres for thyroid cancer since January 2005 (n = 1456) were retrieved, and predefined selection criteria were applied to prevent relevant enrolment biases. A series of 204 patients was finally selected for this study. Measurements: Samples had been stored at −80°C. Tg was measured by fully automated immunometric Elecsys® Tg II and Access® Tg assays in a centralized laboratory. Results: Two hundred and four DTC were finally included. Of these, 10.8% had structural recurrence (sREC), and 81.4% showed no evidence of disease (NED) at the end of follow-up. There was a significant analytical bias between methods that cannot be used interchangeably. Using ROC curve analysis, the best basal and rhTSH-stimulated Tg cut-offs to detect sREC were 0.41 μg/L and 1.82 μg/L for Elecsys® and 0.36 μg/L and 1.62 μg/L for Access® assay, respectively. Using Cox proportional hazard regression, Tg was the only independent predictor of cancer relapse. Conclusions: Using appropriate assay-specific cut-offs, the clinical performance of the Elecsys® Tg II assay was comparable to that provided by the well-established Access® Tg assay.