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Epitope expression in nine commercial kits for the determination of anti-thyroid peroxidase (TPO) antibodies.

Anti-thyroid peroxidase (TPO) antibodies, from patients with autoimmune disease, bind predominantly to two neighbouring, non-identical, conformational domains referred to as domains A and B. In recent years a number of ELISA assays have been developed for the detection of anti-TPO antibodies, however, considerable variation between the different commercial assay kits has been documented in inter-laboratory surveys (UK NEQAS). This investigation assessed the differences between nine commercial ELISA assays currently available in the UK. The anti-TPO kits varied in terms of their imprecision and accuracy and in the density of coated antigen. Recombinant antigen containing kits demonstrated partial destruction of the B epitope, possibly due to the close proximity of both epitope regions in the recombinant molecule. None of the kits expressed only one epitope although there were differences in the degrees of expression of each epitope. Clinicians should be aware of the variability of the numbers generated, when interpreting test results.