Performance Evaluation of the Third-Generation Elecsys FT4 III Assay for Free Thyroxine

Abstract

Background: Roche Diagnostics has recently released the Elecsys FT4 III, Roche's third-generation reagent for free thyroxine. We aim to evaluate the analytical performance of the Elecsys FT4 III. Methods: The precision and linearity of the Elecsys FT4 III assay were evaluated according to Clinical and Laboratory Standards Institute procedures. The results of the third-generation assay were compared with that of Roche's second-generation assay (Elecsys FT II) on a Roche cobas e801 modular analyzer. Results: The coefficient of variation of within-laboratory variation was less than 2.6% for the control materials and patient samples. The linearity was confirmed over a range of 0.41 to 7.52 ng/dL. The mean difference between the second- and third-generation reagents was 0.0026 ng/dL (95% confidence interval, -0.0172 to +0.0224 ng/dL). Conclusions: The analytical performance of the Elecsys FT4 III assay for free thyroxine is clinically acceptable.