Clinical and analytical performance of the liaison cardiac troponin I assay in unstable coronary artery disease, and the impact of age on the definition of reference limits. A FRISC-II substudy.

Abstract

Measurements of cardiac troponins are currently used as the standard for the detection of myocardial injury. None of the current assays complies with the new requirements on assay imprecision as proposed by the European Society of Cardiology/American College of Cardiology. Our aim was to evaluate the clinical and analytical performance of the Liaison cardiac troponin I (cTnI) assay. EDTA-plasma was used, and cardiac troponins were assayed with the first-generation AxSYM assay, the second-generation AccuTnI assay, the third-generation Elecsys assay, and the first-generation Liaison assay. In a 6-day imprecision study, the Liaison cTnI assay had mean CV < or =10% at 0.027 microg/L and < or =20% at 0.015 microg/L. The 99th percentile of the upper reference limit (URL) of a reference population was 0.041 microg/L (age range, 41-76 years). Individuals <60 years had a significantly (P = 0.001) lower 99th percentile, 0.022 microg/L. The FRISC-II study participants with cTnI > or =0.041 microg/L had a poorer outcome relating to death/acute myocardial infarction than those with cTnI <0.041 microg/L (P <0.001). Treatment with low-molecular-weight heparin (dalteparin) or an invasive strategy reduced cardiac events only in patients with concentrations >0.041 microg/L (P = 0.002 and 0.02, respectively). Comparison with the AccuTnI assay showed that a large cohort of the patients with poor prognosis was identified by the AccuTnI assay but not by the Liaison cTnI assay. The Liaison cTnI assay is a sensitive assay with a CV < or =10% at the 99th percentile URL. The ability to detect age-related differences among apparently healthy individuals is unique among today's commercial assays. The results indicate that different assays seem to identify different patient cohorts for cardiac risk in the lower range of cTnI concentrations.