Multicenter evaluation of an automated assay for troponin I.

Background: Cardiac troponin I (cTnI) is a powerful tool to aid in the diagnosis of myocardial infarction and cardiac muscle damage. We describe an assay that overcomes problems of early assays that were often affected by cTnI degradation, assay interference, poor sensitivity, and imprecision.

Methods: The analytical performance of the Access AccuTnI assay (Beckman Coulter) was evaluated at five institutions. Controls, zero calibrator, and diluted patient samples were used to determine precision, detection limit, functional sensitivity, and linearity. The 97.5 and 99 percentiles of a reference population were determined. Common interferents and heterophilic patient samples were tested. Equimolarity was determined by assaying samples with various ratios of free and complexed cTnI. Matched samples drawn into serum, EDTA, lithium heparin, and sodium heparin sample tubes were compared.

Results: Total imprecision (CVs) was 4.0-8.8% between 0.40 and 31 microg/L cTnI. The detection limit was <0.01 microg/L. The 97.5 percentile upper reference limit (URL) was 0.03 microg/L (CV = 20%), and the 99 percentile URL was 0.04 microg/L (CV = 14%). Total CVs of 10% and 20% were seen at and above 0.06 and 0.03 microg/L, respectively. The assay was linear to >60 microg/L and not affected by common assay interferents. An equimolar response was observed with free, complexed, phosphorylated, and dephosphorylated forms of cTnI. Results were 4% lower in serum and 14% lower in EDTA plasma than in lithium heparin plasma (P <0.01), independent of cTnI concentration.

Conclusion: AccuTnI is a sensitive and precise assay for the measurement of cTnI.