Effects of contemporary troponin assay sensitivity on the utility of the early markers myoglobin and CKMB isoforms in evaluating patients with possible acute myocardial infarction

Background: The 2003 American Heart Association (AHA) definition for myocardial infarction (MI) requires an "adequate set" (i.e. at least 6 h between measurements) of biomarkers and specifically troponin for the diagnosis of MI. The aim of the present study was to assess the performance of myoglobin, the CKMB isoforms, and cardiac troponin I (cTnI) in specimens earlier than the requisite 6 h after presentation, in a population originally characterized using World Health Organization (WHO) criteria. Methods: In 1996, 228 acute coronary syndrome patients with an "adequate sample set" had their specimens assayed for CKMB isoforms and myoglobin. In 2003, the same specimens were analyzed with the AccuTnI™ troponin I assay and myoglobin (Beckman Coulter Access® immunoassay). Results: The clinical sensitivities for both myoglobin and the CKMB isoforms were > 90% when the population was classified by WHO criteria. However the sensitivities were < 70% when the ESC/ACC MI definition was used. Analyzing cTnI at earlier time points as long as there was at least 3 h between specimens or at least 1 specimen 6 h from pain onset did not misclassify subjects based on adverse outcomes in the year following their presentation. Conclusion: Contemporary assays for cTnI with increased analytical sensitivity reduce the utility of myoglobin and CKMB isoforms to rule-out an AMI.