Short communicationEffects of contemporary troponin assay sensitivity on the utility of the early markers myoglobin and CKMB isoforms in evaluating patients with possible acute myocardial infarction☆,☆☆
Introduction
In 2003, the American Heart Association (AHA) published criteria based on the ESC/ACC recommendations that operationalized the use of biomarkers to diagnose acute myocardial infarction (AMI) for epidemiology and clinical research studies [1]. In brief, the diagnosis of AMI was considered to be present if cardiac troponin (cTn) measurements were diagnostic in a setting where ischemia was present. A diagnostic set of cTn markers was defined as containing at least 1 elevated measurement from a set of blood samples taken at least 6 h apart (i.e., from an “adequate set” of biomarkers) and manifesting a rising or falling pattern [1]. We have previously reported the increase in the prevalence of AMI using these criteria [2], [3]. For the present study, we sought to determine the potential diagnostic utility of myoglobin and the CKMB isoforms when a contemporary highly sensitive cTn assay is used. In previous studies, using myoglobin and isoforms, less sensitive cTn assays were used or high cutoff values were employed which may have enhanced the apparent value of these markers [4], [5], [6], [7]. This data set also allowed us to assess if earlier measurements of cTn could be used to identify adverse outcomes following the initial event.
Section snippets
Patients and methods
The study population and its characteristics have been previously reported [2], [3], [8], [9], [10]. Briefly, consecutive patients presenting in 1996 to the emergency department of a community hospital with symptoms suggestive of cardiac ischemia were recruited for a retrospective cardiac marker study. The present study includes only those patients who provided at least two specimens with at least one specimen obtained 6 or more hours after presentation, thus conforming to the AHA adequate set
Results
Details on the demographics, in-hospital course treatment, and outcomes for the 228 subjects conforming to the AHA case definition have been previously reported [8]. Briefly this population (median age 67 years) presented early with a median time of 3 h from onset of symptoms to presentation specimen (Table 1). There was a median 5 specimens (in the interval between, and including, the adequate set) used for myoglobin and CKMB isoform analysis. The adjudicated WHO AMI diagnosis in 1996 resulted
Discusssion
The present study confirms earlier work suggesting that the diagnostic utility for myoglobin and CKMB isoforms for the early assessment of AMI has been significantly diminished with the 2000 ESC/ACC criteria [17], [18]. This study is different from others in that the subjects were selected based on their conformity to the AHA case definition. Moreover, this “adequate set” of samples was analyzed with a highly sensitive cTn assay using the 99th percentile cutoff for AMI designation. Previous
Acknowledgments
This work was supported by the Ontario Association of Medical Laboratories' Research Trust Small Grants program. Unrestricted grants for reagents were also contributed by Beckman Coulter Inc. (AccuTnI and myoglobin) and Helena (CKMB isoforms).
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Sources of Support: Ontario Association of Medical Laboratories, Toronto, Ontario, Canada. The AccuTnI and Myoglobin reagent was contributed for the study by an unrestricted grant from Beckman-Coulter Inc.
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See editorial ‘Cardiac troponin monitoring for detection of myocardial infarction: Newer generation assays are here to stay’, F.S. Apple, doi:10.1016/j.cca.2007.01.002 and the ‘Letter to the editor: Authors' Response to Apple Editorial’, P.A. Kavsak, doi:10.1016/j.cca.2007.01.003.