Thyroglobulin immunoassay with a fully automated pretreatment process provides accurate thyroglobulin values in anti-thyroglobulin antibody positive specimens

• Published in: Clinical biochemistry 2023-08, Vol.118, p.110598-110598, Article 110598
• Main Authors: Kitamura, Yoshiyuki, Narita, Sho, Yagi, Shintaro, Aoyagi, Katsumi
• Format: Article
• Language: English
• Subjects: Immunoassay; LC-MS/MS; Pretreatment; Tg-TgAb complexes; Thyroglobulin
• ISSN: 0009-9120; 1873-2933
• DOI: 10.1016/j.clinbiochem.2023.110598

•A new thyroglobulin (Tg) assay with the specimen-pretreatment process showed no TgAb interference.•The new Tg assay facilitated accurate determination of Tg in TgAb-positive samples by disrupting the Tg-TgAb complex.•We validated the accuracy of Tg values obtained by the new Tg assay compared to LC-MS/MS.•TgAb-positive specimens contained various type of Tg-TgAb complexes, and the new Tg assay is unaffected by these complexes. Human thyroglobulin (Tg) is widely used as a tumor marker for recurrence and metastasis of differentiated thyroid cancer (DTC). Currently, serum Tg values are measured using second-generation sandwich immunoassays (2nd-IMA). However, interference by endogenous autoantibodies to thyroglobulin (TgAbs) can lead to false-negative results or falsely low Tg values. Here, we describe a new Tg assay using the immunoassay for total antigen including complex via pretreatment (iTACT) method to prevent TgAb interference and compare it with 2nd-IMA. Tg values were evaluated by three assays: iTACT Tg, Elecsys Tg-II, which is a 2nd-IMA, and LC-MS/MS (Liquid chromatography tandem-mass spectrometry). The ratio of Tg values between each assay was then compared to the Tg value by LC-MS/MS and TgAb titer. Tg immunoreactivity was analyzed by size-exclusion chromatography. Correlation between iTACT Tg and LC-MS/MS using TgAb-positive specimens was good: Passing–Bablok regression with iTACT Tg = 1.084 × LC-MS/MS + 0.831. Correlation between 2nd-IMA and LC-MS/MS showed a relatively lower slope: 2nd-IMA = 0.747 × LC-MS/MS − 0.518. Thus, Tg values determined by iTACT Tg are equivalent to those of LC-MS/MS regardless of TgAb titer, whereas 2nd-IMA gave lower Tg values due to TgAb interference. Tg-TgAb complexes of various molecular weights were verified by size-exclusion chromatography. Tg values measured by 2nd-IMA fluctuated depending on the molecular weight of the Tg-TgAb complexes, whereas iTACT Tg accurately quantified Tg values regardless of the size of the Tg-TgAb complexes. Tg values in TgAb-positive specimens were accurately determined by iTACT Tg. TgAb-positive specimens contain Tg-TgAb complexes of various molecular weights that interfere with Tg value determination by 2nd-IMA, whereas iTACT Tg is unaffected by the presence of Tg-TgAb complexes.