Journal of Korean Endocrine Society 2004;19(1):42-47.
Published online February 1, 2004.
Influence of Anti-thyroglobulin Antibody on the Measurement of Thyroglobulin using the Immunoradiometric Assay.
Byeong Cheol Ahn, Jin Ho Bae, Shin Young Jeong, Ho Yong Park, Jung Guk Kim, Sung Woo Ha, Jaetae Lee, Bo Wan Kim, Kyu Bo Lee
1Department of Nuclear Medicine, Internal Medicine, Kyungpook National Unversity Medical School, Daegu, Korea.
2Department of Surgery, Kyungpook National University Hospital, Kyungpook National Unversity Medical School, Daegu, Korea.
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.
Key Words: Thyroglobulin, Anti-thyroglobulin antibody, Immunoradiometric assay, Accuracy
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