Objectives: Serum thyroglobulin (TG) measurement is essential for long-term monitoring of differentiated thyroid cancer (DTC) following total thyroidectomy. Although isotopic assays are considered the gold standard, non-isotopic methods are increasingly adopted due to logistical advantages. Despite the availability of an international TG standard (certified reference material CRM-457), complete assay standardisation and interchangeability remain unachieved Camel-derived polyclonal anti-TG antibodies have been rarely explored in immunoradiometric assay (IRMA) formats. The in-house IRMA developed using these antibodies was previously validated against a commercial IRMA (TG IzotopR) kit; this study further evaluates its analytical and clinical performance against a standard electrochemiluminescence immunoassay (ECLIA) to assess cross-platform comparability. Material and Methods: In this cross-sectional comparative study, TG levels were measured using an in-house IRMA and Roche Eleusis TG II ECLIA in 157 anonymised leftover serum samples from DTC patients (age 11–79 years; male: female ~1:2), stored at −20 °C. The in-house IRMA uniquely employs camel-derived polyclonal anti-TG antibodies for capture and 125I-labelled monoclonal antibodies for detection. Method comparison was performed using linear regression and Bland–Altman analysis. Results: The analytical ranges were 0.04–500 ng/mL (ECLIA) and 0.1–300 ng/mL (IRMA). A moderate positive correlation was observed ( r = 0.51, n = 157, p <0.001) with the regression equation Y = 0.18X + 4.8, indicating limited agreement. Bland–Altman analysis demonstrated an overall positive bias, with IRMA slightly overestimating TG, particularly at low concentrations. Conclusion: Despite analytical differences, clinical decision-making was not significantly affected. However, consistent use of a single assay is crucial for longitudinal TG monitoring due to limited inter-assay comparability. The in-house IRMA has been used routinely for over 12 years in approximately 50,000 samples, supporting its practical utility. Its cost-effectiveness and sustainability, along with inherent variability between radio isotopic and nonisotopic platforms, underscore the importance of assay consistency in DTC follow-up.
Gholve et al. (Sat,) studied this question.