Comparison of Particle Agglutination Assay and ELISA for Anti-thyroid Autoantibodies

ABSTRACT

BACKGROUND: Measurements of serum anti-thyroglobulin antibody (anti-Tg) and anti-thyroid peroxidase antibody (anti-TPO) are important for the diagnosis of autoimmune thyroid diseases. Although ELISA is most commonly used for the detection of anti-thyroid autoantibodies, other methods like particle agglutination assay (PA) or radioimmunoassay (RIA) are still being used in clinical laboratories. There are few studies about the comparison between PA and ELISA, and we evaluated the validity of these assays in this study. METHODS: We have used three methods, PA (Fujirebio Inc.), ELISA-1 (Zeus Scientific Inc.), and ELISA-2 (Orgentec Diagnostika) for the measurements of titers or concentrations of anti-thyroid autoantibodies. A total of 212 patients belonging to six different disease groups were tested 40 patients for anti-Tg only, 64 for anti-TPO (or anti-microsome) only, and 108 for both antibodies. All test results were compared with each other in six disease groups. RESULTS: Concordance of positive or negative results was obtained in 78.5-97.3% of the samples tested, and positive rates of three methods were similar in autoimmume thyroid disease group. In the comparable concentration range, the correlation coefficients were 0.328-0.820 between the two ELISAs or between ELISA and PA. CONCLUSIONS: Positive or negative decisions by three assay systems have high concordance rates, and antibody levels measured by three methods correlate well in the comparable concentration range. The ELISA-1 shows less non-specific reactions, better discrimination in low level of autoantibodies, and the highest positive rate in autoimmume thyroid disease group.