Analytical Characteristics of the AxSYM Cardiac Troponin I and Creatine Kinase MB Assays

Abstract

The use of biomarkers for the detection of myocardial infarction (MI) has been recently redefined by the American College of Cardiology, the American Heart Association, and the European Society of Cardiology (1)(2). These consensus statements replace earlier recommendations by the National Academy of Clinical Biochemistry and IFCC that proposed the use of two separate decision limits: a higher cutoff for detection of acute MI (AMI) and a lower cutoff for detection of myocardial injury of lower degree, as observed in unstable angina pectoris (3)(4). The new consensus statements redefined MI in that even small areas of necrosis are considered as MI. Cardiac troponins represent cardiac-specific molecules almost undetectable in the blood of healthy individuals. In addition, current immunoassay techniques for quantification of troponins in blood enable identification of small cardiac injury (1)(2). Cardiac troponins have been designated the preferred biomarkers for the diagnosis of AMI. If cardiac troponins are not available, testing for creatine kinase (CK)-MB, although less cardiospecific, can be used (2). Myocardial injury is assumed if measured concentrations of the respective biomarkers are above the 99th percentile of a healthy reference group, provided that the imprecision (CV) of the assay used is ≤10% at the decision limit (1)(2). Using the new guidelines, we evaluated the AxSYM Troponin-I and CK-MB assays. Cardiac troponin I (cTnI) and CK-MB were measured by microparticle enzyme immunoassays on a routine AxSYM analyzer (Abbott Laboratories) as described elsewhere (5). The minimum detectable concentration (MDC) of the AxSYM cTnI was evaluated as the mean + 2 SD of zero calibrator in 20 replicates. Total imprecision was assessed by …