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DOI: 10.1055/s-2008-1065320
© Georg Thieme Verlag KG Stuttgart · New York
Second-generation Thyrotropin Receptor Antibodies Assay and Quantitative Thyroid Scintigraphy in Autoimmune Hyperthyroidism
Publication History
received 22.05.2007
accepted after second revision 13.12.2007
Publication Date:
31 March 2008 (online)
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Abstract
Graves' disease (GD) is characterized by circulating TSH receptor antibodies (TRAb), and so-called hyperthyroid autoimmune thyroiditis (H-AIT) generally shows negative TRAb results with first-generation assays. However, a positive titer was observed in up to 13% of patients with euthyroid or hypothyroid autoimmune thyroiditis (AIT) by second-generation TRAb assays, and a larger increase is expected in hyperfunctioning forms. A thyroid 99mTc-pertechnetate uptake (TcTUs) cutoff of 2% previously was shown to accurately discriminate between GD and H-AIT. Here we evaluated the relationship between second-generation TRAb assays and TcTUs in 139 patients with untreated autoimmune hyperthyroidism. An increase in TRAb levels was found in 114 of 139 patients (82%). All patients with TcTUs >2% and 66% of those with lower values had positive TRAb measurements. When the cutoff was increased to 5.9 U/l, positive TRAb occurred in 92.6% of those having higher TcTUs and in 1.4% of those with lower TcTUs. TRAb levels significantly increased in patients with TcTUs higher than 2% as compared with those having lower values, while no differences occurred in patients with TcTUs ranging from 0 to 1%, from 1.1 to 1.5%, or from 1.6 to 2%. A significant relationship between TRAb and TcTUs (as well as fT3, fT4, and thyroid volume) was found. TcTUs, fT4, fT3, and thyroid volume significantly increased in patients with positive TRAb (cutoff 1.5 U/l) compared with those testing negative. Our data indicate that a large proportion of patients with hyperthyroidism and hypoechoic thyroid, including those previously diagnosed as having H-AIT, actually have circulating TRAb. TRAb levels predicate the degree of iodine uptake (as measured by TcTUs) and thyroid hyperfunction. The role of baseline TRAb measurement by second-generation assays to predict patients’ outcome needs to be further evaluated and compared with TcTUs in prospective studies.
Key words
thyrotropin receptor antibodies - hyperthyroidism - quantitative thyroid scintigraphy - radio-receptor assay - 99mTc-pertechnetate
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Correspondence
Dr. med. L. Giovanella
Department of Nuclear Medicine
PET-CT Center and Thyroid Unit
Oncology Institute of Southern Switzerland
6500 Bellinzona
Switzerland
Phone: +41/91/811 86 72
Fax: +41/91/811 82 50
Email: luca.giovanella@eoc.ch