Development of a radioimmunoassay for autoantibodies to thyroid peroxidase (TPO) in human serum

Purpose: Autoantibodies to thyroid peroxidase (TPO), the thyroid 'microsomal' antigen, are widely utilized in the diagnosis of human autoimmune thyroid disease. The purpose of our work is to develop a useful radioimmunoassay for large scale routine measurement of autoantibodies to TPO in human serum. Methods: the assay is based on autoantibody inhibition of binding of 125I-labeled TPO to an anti-TPO monoclonal antibody coupled with poly-acrylamide macroparticles. Standards containing anti-TPO monoclonal antibody were employed. Serum samples of known anti-TPO body positive (n=38) and negative(n=55) were measured by the new assay. To evaluate the specificity of the assay, several serum samples with high concentration of anti-thyroglobulin (Tg) autoantibody were measured again following absorption with thyroglobulin. Results: Unlike most of other immunoassay for anti-TPO autoantibodies, the new assay has no need for sample dilution. The detection limit of the new assay was 4.4 U/ml and the within-and between assay coefficients of variation (CVs) ranged from 4.7% to 9.8% and from 9.4% to 14.4% respectively. No influence of anti-Tg autoantibodies on the assay was observed. The value for the samples of known autoantibodies to TPO positive or negative were ranging from 12.6 to more than 3000 U/ml and from to 8.1 U/ml respectively. Conclusion: This new assay is sensitive, not affected by anti-thyroglobulin autoantibodies, easy to perform and has no need for sample dilution. Therefore, it is applicable for large-scale routine measurement of autoantibodies to TPO. (authors)