Analytical evaluation of anti-thyroid peroxidase II assay on Atellica IM analyser: what to expect when changing methods

Abstract Objectives The anti-TPO assays are known for the method variability. The new aTPOII assay (Siemens Healthineers) has a different TPO antigen and detecting antibody source and it is also traceable to another international standard compared to the old aTPO assay (Siemens Healthineers). The aims of this study were to verify the new assay through a method comparison (n=860) with the old aTPO assay from the same manufacturer and to verify the reference range (n=60) on Atellica Immunoanalyzer (Atellica IM). Methods A total of 860 patient serum samples were measured using the Atellica IM aTPO and Atellica IM aTPOII assays and the positive percent agreement, negative percent agreement, and overall percent agreement (OPA) were calculated along with their corresponding 95 % confidence interval (CI). The reference interval verification on 60 euthyroid patient samples was done. Results In view of the substandard quantitative agreement between methods, a qualitative assay comparison was performed and demonstrated that there was good sensitivity (81.5 %; 95 % CI: 77.1–85.3 %), specificity (99.6 %; 95 % CI: 98.6–99.9 %) and OPA (92.6 %; 95 % CI: 90.6–94.1 %). The computed Cohen kappa was 0.84 (95 % CI: 0.80–0.88) which reflects a very good strength of qualitative agreement. The manufacturer’s reference interval (cut-off ≤13.8 U/mL) was verified and confirmed. Conclusions Using the new aTPOII assay more patients will have negative results. Even though assays claim to be referenced to the corresponding WHO International reference preparation, this standardization does not ensure cut-offs and/or results that are identical and does not guarantee method agreement and assays could not be used interchangeably.