Thyroglobulin Measurement by Liquid Chromatography–Tandem Mass Spectrometry May be Useful in Post-operative Differentiated Thyroid Cancer Patients With Undetectable Immunometric Thyroglobulin and Detectable Non-elevated Anti-thyroglobulin Antibodies

  • Background: plasma thyroglobulin (Tg) is essential for the prognostication of differentiated thyroid cancer (DTC). Plasma Tg by immunometric assay (Tg-IMA) may be falsely low in patients with detectable plasma anti-thyroglobulin antibodies (Tg-Ab). Measurement of plasma Tg by liquid chromatography–tandem mass spectrometry (Tg-LCMS) may be more reliable in the presence of elevated Tg-Ab. We set out to compare the performance of plasma Tg-LCMS and Tg-IMA in patients with DTC.

    Methods: retrospective chart review. 

    Results: of 34 patients, stage I, II, III and IVa disease were documented in 30, 2, 1 and 1 patients respectively. 3/34 patients had structural evidence of disease and 1 patient had a biochemically indeterminate response, while the remaining 30 patients had an excellent response to therapy. The mean ± SEM plasma Tg were 2.58 ± 1.10 mcg/L (LCMS) and 1.98 ± 0.92 mcg/L (IMA) with no significant difference in the means [P-value 0.7]. The two tests displayed a strong positive correlation to each other [Pearson’s correlation coefficient 0.99, P-value < 0.001]. Of the patients with detectable but not elevated Tg-Ab, there were 3 patients (8.9%) with undetectable plasma Tg-IMA who had detectable Tg-LCMS. Plasma Tg-LCMS and Tg-IMA were both undetectable in the 3 patients with structural evidence of disease.

    Conclusions. In patients with DTC and negative plasma Tg-IMA, Tg-LCMS is detectable in up to 8.8% of patients with detectable non-elevated Tg-Ab and may lead to further investigations. However, for patients with detectable Tg-IMA, the measurement of Tg-LCMS is of little benefit regardless of Tg-Ab levels. 

 

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