Objectives: Thyroglobulin (Tg) is an established tumor marker for differentiated thyroid carcinoma (DTC) patients. However, Tg immunoassays can be subject to autoantibody (TgAb) interference resulting in incorrect Tg values. Tg measurement with liquid chromatography-tandem mass spectrometry (LC-MS/MS) could be promising in patients with TgAbs. In this study, we compared a Tg immunoradiometric assay (Tg-IRMA) and a Tg-LC-MS/MS analytically in the presence of TgAbs. Furthermore, we evaluated the clinical concordance between both assays in DTC patients with lower TgAbs titers (<10 U/ml) TgAbs during 131I ablation therapy.
Methods: 118 DTC patients diagnosed between 2006 and 2014 in a University Medical Center were followed up with the Tg-IRMA (Thermo Fischer Scientific) and ARCHITECT Anti-Tg (Abbott Laboratories) assays. TgAbs ≥ 10 U/ml were defined as potentially interfering. We re-analyzed their samples with a sensitive Tg-LC-MS/MS method (Labcorp, North Carolina, USA, limit of quantification of 0.02 ng/ml). Passing-Bablok regression analysis was performed on samples obtained during 131I ablation therapy and follow-up.
Results: In 304 samples with lower titer TgAb titers, good agreement was found between both Tg assays (slope of 1.09 (95% CI 1.05 - 1.16)). Fifty-five samples with potentially interfering TgAbs showed higher Tg-LC-MS/MS values than Tg-IRMA (slope of 1.45 (95% CI 1.12->>100)). For patients (n = 91) with lower TgAb titers at the time of 131I ablation therapy, the clinical concordance of both Tg assays was 91.2%.
Conclusions: In DTC patients with lower titer TgAbs, Tg-IRMA is a reliable and useful tumor marker. In DTC patients with potentially interfering TgAbs, Tg-IRMA values are decreased due to TgAb interference.
10 Sep 2022 - 13 Sep 2022