The BI-EIA-THYROID-ANTI-TPO plates are coated with human Thyroid Peroxidase. Serum to be tested is diluted and incubated with the precoated plate. In this step TPO specific antibodies arebound to the immobilized human Thyroid Peroxidase. Non specific antibodies are removed by washing. Anti-human IgG conjugated to horseradish peroxidase (HRP)is added and incubated. In this step the HRP-conjugate is bound to the prebound antigen-anti body complex. Unbound conjugate is removed by washing. The presence of bound enzyme indicating the presence in the specimen of specific antibodies is revealed by a color change in TMB- substrate solution