The comparison and validity of troponin I assay systems in diagnosing myocardial ischemic injury after surgical coronary revascularization

OBJECTIVE: A prospective observational study was conducted to test the agreement between 2 commercially available automated cardiac troponin-I immunoassay systems (Opus Plus, Behring Diagnostics UK Ltd, Hounslow, UK; AxSYM, Abbott Laboratories, Abbott Park, IL) and to determine a normal reference range and threshold value indicative of perioperative myocardial infarction (PMI) after elective coronary artery bypass graft (CABG) surgery for the Opus Plus system. DESIGN: Prospective, observational study. Setting : Single institution, cardiothoracic specialty hospital. PARTICIPANTS: Seventy patients undergoing elective CABG surgery. INTERVENTIONS: After institutional review board approval, patients received standardized anesthetic, surgical, and myocardial preservation techniques. Serial electrocardiographs, creatine kinase-MB, troponin-I, and perioperative outcome data were collected. Correlation between the immunoassay systems was tested using 124 duplicate samples from the first 18 patients. The normal reference range and threshold value indicative of PMI were tested for the Opus Plus system using duplicate samples from all 70 patients. MEASUREMENTS AND MAIN RESULTS: Peak troponin-I concentrations (median [interquartile range]) differed significantly when measured by the Opus Plus and AxSYM immunoassay systems (5.61 [3.20-22.35] microg/L v 46.50 [14.55-70.95] microg/L, respectively; p < 0.001). There was clear proportional bias that was corrected with log transformation of the raw data. By using confidence interval and receiver operating characteristic curve analysis, the authors showed that a value > or =15 mug/L was indicative of PMI (Opus Plus system) and accordingly report a 35.7% (2.9% Q-wave) overall incidence of PMI in this study population (n = 70). CONCLUSIONS: These data highlight differences between commercially available troponin-I assay systems. The authors recommend that each institution establish a local reference range and threshold indicative of perioperative myocardial infarction for its specific patient population and assay system and provide sample methodology.