Comparison of three different assays for measuring thyroglobulin and thyroglobulin antibodies in patients with chronic lymphocytic thyroiditis

To evaluate how thyroglobulin (Tg) and thyroglobulin antibody (TgAb) results compare among different chemiluminescence methods. Serum specimens from 153 patients with thyroiditis and 127 apparently healthy individuals were collected at the Peking Union Medical College Hospital from September 2014 to December 2014. TgAb and Tg levels were analyzed by using three different platforms manufactured by Roche, Beckman, and Siemens. The χ2 test was performed to analyze the TgAb results from the different methods. Passing-Bablok regression equations and Bland-Altman plots were used to estimate the relationship and bias among the Tg results obtained with the different analyses. The overall coincidence rates for the TgAb results were 82.9% between the Beckman and Roche methods, 78.6% between the Siemens and Roche methods, and 81.1% between the Siemens and Beckman methods. The borderline positive coincidence rate among the different TgAb methods was very poor (9.1–24.2%). Of the 280 samples, the TgAb results for 26.4% of the samples differed among the three CLIA platforms. A good linear relationship among the Tg levels was shown in TgAb-negative subjects analyzed with the different CLIA systems. However, for TgAb-positive subjects, the linear relationship of the Tg levels measured with the Siemens system, compared with the other two systems, was poor. Bland-Altman plots demonstrated significant differences among the different Tg assays. Current Tg and TgAb methods are highly variable and cannot be used interchangeably.