Multicenter Evaluation of the TOSOH AIA-Pack Second-Generation Cardiac Troponin I Assay

The redefined biochemical criterion proposed to diagnose myocardial infarction (MI) necessitates the availability of highly sensitive and precise cardiac troponin assays (1). In general, a substantial improvement in the analytical performance is offered by the newer assays. In this multicenter study, we evaluated one of these improved cardiac troponin I (cTnI) assays, performed on the AIA 21 immunoassay system (TOSOH Corp.), using criteria tailored in accordance with IFCC recommendations (2). The AIA-Pack second-generation cTnI assay uses a combination of two monoclonal antibodies, one directed to amino acids 41–49 of the cTnI molecule and another directed to amino acids 87–91. A human cardiac ternary troponin ITC complex is used as calibration antigen. The minimum detectable cTnI concentration was defined as the value corresponding to a signal 3 SD greater than the mean of 20 replicates of the zero calibrator in a single run. Buffered stock solutions of both free cTnI and troponin IC complex (Scripps Laboratories) were serially diluted in AIA-Pack diluent and tested to estimate the degree of equimolarity. Four cTnI-rich serum pools (native concentrations, ∼2.5 to ∼100 μg/L) were serially diluted with serum pools having cTnI below the detection limit or with the manufacturer’s diluent. The undiluted sample and four dilutions were assayed in duplicate, and the curve obtained was tested for linearity (3).