MEASUREMENT OF TSH RECEPTOR ANTIBODIES IN PATIENTS WITH THYROID-DISORDERS

In order to measure TSH receptor antibodies (TRAb) we tried to set up a radioreceptor assay using human thyroid membranes. Due to lack of ap propriate binding activity of the material obtained, we decided to use a kit which provides solubilized porcine membrane-receptors to TSH in stead of human membranes, as well as calibrators that have been standa rized in a receptor assay against MRC LATS std B. With these reactives we have measured TRAb in sera from 7 normal controls (C), 54 thyrotox ic patients (43 diffuse goiters [BDH], 8 multinodular goiters [BHM] an d 3 Subacute Thyroiditis [TSA]), 3 patients with Hashimoto's Thyroidit is (TH) and in 6 non-hyperthyroid Graves ophtalmopathy patients. Measu rement were initially performed using calibrators and the results expr essed as U/L; since a very good correlation between the expression U/L and the calculated Inhibition Index (I.I.) was found (r = 0.99, n = 1 5, p < 0,001), results are shown using latter. In C mean +/- SD value for I.I. was 3.4 +/- 2.37%, so we decided to use, as cut off criteria for differentiating between normal and abnormal results, the figure 11 %, which represents the mean +/- 3 SD. According to this, 93% of BDH h ad elevated TRAb activity while only slightly more than one third of M BH had elevated values, this difference being highly significant (p < 0,0001); both TSA and TH patients showed low TRAb activity while all G raves ophtalmopathy pts had elevated values, thus suggesting that they had a latent disease. We concluded that the methodology that is adequ ate and practical for clinical purposes. Our results show that measure ment of TRAb activity is useful in establishing the etiology of hypert hyroidism in an individual patient so we feel that it should be of com mon use in most, if not in all, thyrotoxic patient. Also it provides h elp in the differential diagnosis of patients with exoftalmus of unkno wn etiology. Its usefulness remains to be proved in the follow-up of B DH pts after been treated with antithyroid drugs.