Inter-platform variability of TgAb, TPOAb and TRAb immunoassays: analytical agreement and consequences for antibody positivity

OBJECTIVES: To compare the agreement of anti-thyroglobulin (TgAb), anti-thyroid peroxidase (TPOAb), and thyrotropin receptor antibody (TRAb) results across four automated immunoassay platforms, and to assess the impact of assay variability on positivity rates in different clinical populations. METHODS: A total of 742 serum samples were collected from Shanghai Seventh People's Hospital between September and December 2025. TgAb, TPOAb, and TRAb levels were measured using four chemiluminescence immunoassay platforms (Roche e 601, Mindray CL-8000i, Abbott Alinity i, and Snibe MAGLUMI X3). RESULTS: Significant inter-assay variability was observed. Passing-Bablok regression demonstrated proportional differences among platforms, with slopes ranging from 0.1935 to 2.8455 for TgAb, 0.6486 to 2.1930 for TPOAb, and 0.7918 to 1.2698 for TRAb. Bland-Altman analysis revealed wide limits of agreement, particularly for TgAb and TPOAb. TgAb and TPOAb positivity rates were highest in autoimmune thyroiditis, but showed marked inter-platform variation across all disease groups (Cochran's Q, p<0.001). TRAb positivity was consistently high in Graves' disease (89.81-98.15 %) and low in other groups (3.00-15.18 %), with relatively better agreement across platforms. CONCLUSIONS: Inter-assay variability exists in thyroid autoantibody measurements, particularly for TgAb, leading to inconsistent positivity rates. Platform-dependent differences may influence interpretation of thyroid autoantibody results and emphasize the need for assay harmonization.