The use of other markers

Many studies previously done suggest that because increases in short-acting markers, such as myoglobin or fatty acid binding protein, or in the past, isoforms of CK increase more rapidly than troponin that they may save time in the ED

or chest pain clinic [27,29,30,72]. The value of this approach is predominantly to exclude infarction at an earlier point in time because these analytes lack cardiac specificity and often are falsely positive. Thus, what has been relied on is their negative predictive value, which is fairly high. A critical issue in this area has been that many of these studies done evaluating these analytes have used insensitive troponin assays or high cutoff values despite the use of sensitive assays. Recent data suggest that as one begins to use cutoff values, such as the 99th percentile and 10% CV that the difference in timing associated with these other laboratory tests becomes more modest than previously suggested (Fig. 8) [31]. A similar approach relying on the negative predictive value of nonele-vated values has been taken with IMA [32-34], which is a marker of ischemia rather than necrosis. The influence of more sensitive troponin assays on the timing of elevations can also influence the amount of time saved with this ana-lyte. The time saved which is now more modestly worthwhile compared with the cost and the confounds associated with the frequent false positives. The studies done with IMA have used more contemporary troponin assays and cutoff values [32-34] but continuing issues exist concerning the proper cutoff values for the test, analytic issues related to pH and lactate [35] and concern

Fig. 8. Sensitivity of cTnl, CK-MB and myoglobin over time using modern prognostic cutoff values. Note that 0.7 ng/ml is the 99th percentile for the assay used. From Eggers KM, Oldgren J, Nordenskjold A, et al. Diagnostic value of serial measurement of cardiac markers in patients with chest pain: limited value of adding myoglobin to troponin I for exclusion of myocardial infarction. Am Heart J 2004;148:574-81;with permission.

Fig. 8. Sensitivity of cTnl, CK-MB and myoglobin over time using modern prognostic cutoff values. Note that 0.7 ng/ml is the 99th percentile for the assay used. From Eggers KM, Oldgren J, Nordenskjold A, et al. Diagnostic value of serial measurement of cardiac markers in patients with chest pain: limited value of adding myoglobin to troponin I for exclusion of myocardial infarction. Am Heart J 2004;148:574-81;with permission.

about what should be done if a patient has an elevated IMA without an elevated troponin. Accordingly, a much simpler, more cost-effective paradigm would be to measure troponins on two occasions: (1) when the patient first presents and (2) 6 hours later or earlier if the onset of symptoms is totally clear. Additional data likely will shorten this time somewhat also. This paradigm would be a highly sensitive, highly specific, and cost-effective way of triage but requires thoughtful consideration of the etiologies of the potential troponin elevations, some clinical judgment, and a knowledge of the assays that are used locally.

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