PREVALENCE OF THYROID-HORMONE AUTOANTIBODIES IN HEALTHY-SUBJECTS

OBJECTIVE The prevalence of thyroid hormone autoantibodies in patients with thyroid disorders has been well described, although the results have been variable. However, the prevalence of thyroid hormone autoant ibodies in apparently healthy subjects remains unknown and its determi nation was the main objective of this study. SUBJECTS AND METHODS Sera obtained from 880 healthy subjects (365 men and 515 women) were exami ned for thyroid hormone autoantibodies by immune precipitation using r adiolabelled thyroid hormones or thyroid hormone analogues. RESULTS An ti-triiodothyronine (T3) and anti-thyroxine (T4) antibodies were detec ted in none (0%) and in 3 (0.34%), respectively, of the 880 individual s studied using radiolabelled thyroid hormones. Similar tests in 385 h ealthy subjects using radiolabelled thyroid hormone analogues (polyami nocarboxy T3 and T4) showed the presence of anti-T3 and anti-T4 antibo dies in 3 (0.78%) and in 4 (1.04%), respectively. None of the subjects had both anti-T3 and anti-T4 antibodies, Thus, the prevalence of anti -T3 or anti-T4 antibodies among healthy population was concluded to be as high as 1.8%. Radiolabelled thyroid hormone analogue binding to pu rified immunoglobulin G (IgG), with or without the addition of an exce ss of unlabelled thyroid hormones, confirmed specific binding of thyro id hormones to the thyroid hormone autoantibody-positive IgGs. The pre sence and class specificity of thyroid hormone autoantibodies was conf irmed by the Ouchterlony immunodiffusion/autoradiography method, which showed biphenotypic heavy chain (IgG and IgA) and kappa (kappa) light chain specificities. Serum concentrations of free thyroid hormones an d TSH in thyroid hormone autoantibody-positive sera were within the no rmal range. CONCLUSIONS These results indicate that the occurrence of thyroid hormone autoantibodies among the healthy Japanese population i s fairly common. However, interference of thyroid hormone autoantibodi es in the radioimmunoassay of free thyroid hormones is exceptional.