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TSH‐receptor antibody measurement for differentiation of hyperthyroidism into Graves' disease and multinodular toxic goitre: a comparison of two competitive binding assays
Author(s) -
Pedersen Inge Bülow,
Knudsen Nils,
Perrild Hans,
Ovesen Lars,
Laurberg Peter
Publication year - 2001
Publication title -
clinical endocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.055
H-Index - 147
eISSN - 1365-2265
pISSN - 0300-0664
DOI - 10.1046/j.1365-2265.2001.01347.x
Subject(s) - trab , graves' disease , medicine , euthyroid , endocrinology , receptor , autoantibody , thyroid , antibody , immunology
OBJECTIVES Graves' disease is characterized by stimulating autoantibodies to the TSH‐receptor (TRAb). The aim of this study was to compare the performance of a new TRAb assay based on competitive binding to recombinant human TSH‐receptors (H‐TRAb) with an assay employing purified porcine TSH‐receptors (P‐TRAb). Furthermore, to evaluate the applicability of the H‐TRAb assay to discriminate between patients with hyperthyroidism due to Graves' disease (GD) and multinodular toxic goitre (MNTG). DESIGN AND MEASUREMENTS H‐TRAb and P‐TRAb were measured in patients with newly diagnosed hyperthyroidism due to GD ( n = 106) and MNTG ( n = 94). For comparison, TRAb was measured in patients with primary autoimmune hypothyroidism, euthyroid subjects with an enlarged thyroid gland by ultrasound, and healthy controls ( n = 100 for each group). Patients were consecutively included from a population survey. RESULTS If the cut‐off values recommended by the manufacturer for TSH‐receptor antibody positivity were used for evaluation, the sensitivity of the H‐TRAb assay vs. the P‐TRAb assay in diagnosing GD was: 95·3/67·9% ( P < 0·001). Specificity was (H/P‐TRAb): 99/99%. The sensitivity of P‐TRAb was increased if the upper 97·5% limit of measurements in controls was used as cut‐off (H‐TRAb vs. P‐TRAb: 95·3/80·2%, P < 0·001). Specificity (H/P‐TRAb): 98/98%. The difference between assay performance may partly be due to a better technical performance of the H‐TRAb assay with more reliable results in the low range of measurements. However, even in GD patients with clearly measurable TRAb, 25% had a P‐TRAb < 50% of the value expected from the H‐TRAb measurement. This suggests that a subgroup of patients produce TRAb with a higher affinity for the human than the porcine TSH receptor. A relatively high proportion of patients with MNTG were TRAb positive (H‐TRAb/P‐TRAb: 17/9%). Characteristics of H‐TRAb positive and negative MNTG patients were compared. There was no difference between size of thyroid gland and number of nodules by ultrasonography. H‐TRAb positive patients had significantly higher serum T4 and T3 and a greater number were TPO‐Ab positive. CONCLUSIONS H‐TRAb diagnosed Graves' disease with a high sensitivity and specificity than P‐TRAb. The high occurrence of TRAb in multinodular toxic goitre might in part reflect an overlap between Graves' disease and multinodular toxic goitre in some patients.