Comparative multicentre study of a panel of thyroid tests using different automated immunoassay platforms and specimens at high risk of antibody interference.

The introduction of automation for immunoassays in recent years has brought about important and evident improvements in assay precision. Increasing standardization and comparability between platforms should enable the development of clinical guidelines and diagnostic algorithms for appropriate clinical decision making. A continuing source of variation between different automated immunoassay platforms is the sporadic effect of interfering antibodies or substances, thus causing aberrant results not supporting the patient's clinical status. The aim of this study was to describe current thyroid panel variation between automated immunoassay platforms including population specimens at risk of antibody interference. A multisite design with laboratories in three different countries using four different automated immunoassay platforms (Roche-Boehringer Mannheim Elecsys (Italy), Roche-Boehringer Mannheim ES300 (Wales), Bayer Immuno 1 and the Bayer ACS:180 evaluated the thyroid panel of thyrotropin (TSH), triiodothyromine (T3), free thyroxine (FT4) and free triiodothyronine (FT3). A common set of 158 randomly selected patient samples of non-thyroid and thyroid disorders, with and without treatment, was tested. Included were 62 patient samples at risk for endogenous antibody interference with high antimicrosomal antibody, anti-TSH receptor antibody and increased rheumatoid factor sub-populations. Across all controls and between platforms, precision measurements were comparable and varied between 0.7% and 12.8% for TSH, 2.8% and 13% for FT4, 1.8% and 10.5% for FT3 and 3.1% and 16% for T3 assay. Acceptable correlation and reproducibility were found between the three Bayer Immuno 1 platforms at each country's site with all four thyroid panel assays demonstrating r-values of 0.989 to 1.000 and slopes of 0.915 to 1.078. Comparisons between the different platforms showed acceptable correlation for all thyroid panel assays. Specimens containing rheumatoid factor were associated with a significantly increased variation between systems for the FT4 and FT3 assays (p < 0.01). This effect did not appear to be selective for a given platform. For specimens with raised autoimmune antibodies and therefore at risk of assay antibody interference, no variation could be observed between the platforms.