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Abstract
Liewendahl K, Melamies L, Helenius T, Karonen S-L, Liljeström E, Valimäki M, Weber T. Automated and manual serum free thyroxine assays evaluated with equilibrium dialysis. Scand J Clin Lab Invest 1994; 54: 347-51.
Two fully automated serum FT4 assays (Ciba Corning: ACS-180; Abbott Diagnostics: IMx) and two manual/semiautomated assays (Wallac: Delfla; Diagnostic Products Corp.: Coat-A-Count) were compared with a FT4 reference method based on equilibrium dialysis (ED) using routine clinical samples (n = 105-150). For the full range of FT4 concentrations the correlation with ED was good (r = 0.932-0.959), except for Coat-A-Count (r = 0.852), a single-step analogue-type method. Analytical inaccuracy of the automated methods at low FT4 concentrations was revealed by the differential plot: the IMx assay overestimated concentrations < 10pmoll−1 and the ACS-180 assay concentrations < 6pmo11−1. The between-assay CVs for the automated methods were not better than for the non-automated assays indicating problems of calibration curve stability for the automated assays.