Performance characteristics of loci method for measuring cardiac troponin I on the dimension EXL

OBJECTIVE: To define the performance characteristics of the LOCI(®) method for cardiac troponin I on the Dimension EXL system. DESIGNS AND METHODS: Three different levels of commercial control (mean concentrations 0.426, 1.42, and 18.64 µg/L) were used for the imprecision study, quantifying separately within-run and between-run over 20 days. The limit of blank (LoB) and limit of detection (LoD) were assessed with 20 replicates of a sample without troponin I. Linearity was assessed by regression analysis. In addition, we studied inaccuracy, carry-over and limit of quantitation and conducted a method comparison with the Stratus CS (n=69). The reference interval was determined in 146 healthy blood donors using non-parametric method. RESULTS: The within-run imprecision (coefficient of variation [CV], %) obtained at each level was 2.4, 1.4% and 2.2%, while the between-run imprecision (CV,%) was 3.3%, 2.9% and 2.5%. Total imprecision was 4.06%, 3.3% and 3.4% for each control level. The limit of quantitation which corresponds to the troponin I concentration at which CV=10% was 0.05 µg/L. Method comparison with the Stratus CS assay produced the equation: Dimension EXL=−0.002698+1.0233(⁎)(Stratus CS) with a confidence interval from −0.01562 to 0.00626 for the intercept and (0.979 to 1.0875) for the slope. The 99th percentile obtained for the reference population was 0.047 µg/L. CONCLUSIONS: The LOCI method for cardiac troponin I on the Dimension EXL meets all guidelines recommended criteria referring to limit of quantitation, imprecision and shows excellent transferability with the Stratus CS method.