Influence of Anti-thyroglobulin Antibody on the Measurement of Thyroglobulin using the Immunoradiometric Assay / 대한내분비학회지

ABSTRACT

BACKGROUND: Serum thyroglobulin(Tg) is a valuable and sensitive tool needed in the follow-up of patients with differentiated thyroid cancer(DTC), but antithyroglobulin antibody(Anti-Tg), common in patients with DTC, can interfere with the assay for Tg. In this study, we evaluated the influence of Anti-Tg on the measurement of Tg using the immunoradiometric assay(IRMA). METHODS: In using ELSA-hTg in vivo test(CIS international, Schering, France), a solid phase two-site IRMA was used to measure Tg(23.5ng/mL, 62.5ng/mL) under the absence or presence of three concentrations of Anti-Tg(25U/mL, 50U/mL, 100U/mL). We also performed Tg measurement using patients serum that was mixed with patients serum containing high Anti-Tg. ANOVA and Scheffe tests were performed to evaluate the effect of Anti-Tg on Tg IRMA, and an inverse regression was made to calculate the level of Tg from measured Tg and used Anti-Tg levels and also to assess the degree of effect of anti-Tg on Tg IRMA. RESULTS: In measuring Tg using the standard solution, the presence of Anti-Tg resulted in a falsely suppressed Tg value. The IRMAs for 23.5ng/mL of the standard Tg solution resulted in 24.5+/-.1 ng/mL under no Anti-Tg, 11.8+/-.4ng/mL under 25U/mL of Anti-Tg, 7.7+/-.1ng/mL under 50U/mL of Anti-Tg, and 4.5+/-.4ng/mL under 100U/mL of Anti-Tg. IRMAs 62.5ng/mL of the standard Tg solution resulted in 65.9+/-.7ng/mL under no Anti-Tg, 36.3+/-.2ng/mL under 25U/mL of Anti-Tg, 23.7+/-.7ng/mL under 50U/mL of Anti-Tg, and 14.0+/-.0ng/mL under 100U/mL of Anti-Tg. (ANOVA test, p=0.000). The degree of suppression of the measured Tg value was positively correlated with the Anti-Tg level (Quadratic model regression, Sig T=0.000). The presence of Anti-Tg also resulted in a falsely suppressed Tg value for the Tg measurement using patient's serum. CONCLUSION: The presence of Anti-Tg could consist of the use of Tg as a tumor, therefore Anti-Tg should be measured in all patients diagnosed with DTC. The interpretation of the Tg level must be performed with extreme caution in patients with Anti-Tg.