New Biochemical Tools for Diagnosing Acute Coronary Syndromes: Impact on Patient Outcomes and Resource Utilization in Hospitals
W. Frank Peacock
This article reviews the value of myoglobin, troponins, and creatine kinase, MB fraction (CK-MB) in diagnosis, risk stratification, and prognosis in patients presenting to hospital emergency departments (ED) with symptoms suggestive of acute coronary syndromes. Because the three markers differ in specificities and their sensitivities vary with time after the onset of chest pain, the authors suggest that serial measurements for all three markers by point-of-care methods will optimize patient outcomes and reduce resource utilization. The rationale for this strategy is examined from the viewpoint of ED physicians who must make diagnoses, risk stratify patients, and make treatment decisions in patients presenting with non-diagnostic ECGs. The articles reviewed show that despite its elevation in renal and skeletal muscle disease, myoglobin offers more sensitivity for the early diagnosis of acute myocardial infarction (MI) than either CK-MB or troponins. The most important characteristic of myoglobin is its high negative predictive value for acute MI. Myoglobin also shows promise as a non-invasive marker of reperfusion status in patients undergoing thrombolytic therapy. Articles are examined which indicate that cardiac troponin I and troponin T, despite standardization problems for troponin I, offer greater specificity than either CK-MB or myoglobin in detecting MI, particularly when measurements are made with third-generation assays at presentation and 6-12 hours later. Because troponin elevation persists for days after CK-MB and myoglobin have returned to normal, troponins have high sensitivity for detecting MIs in patients presenting days after the onset of chest pain. The use of troponins in evaluating prognosis in patients with acute coronary syndromes - including those at low risk for MI, without ECG changes, triaged to a chest pain unit, with renal disease, undergoing noncardiac surgery, and undergoing treatment for MI - is discussed in detail because troponin concentrations may help to guide ED clinicians in diagnosis, risk stratification, and treatment. Finally, key reports suggesting that rapid serial measurements of myoglobin, troponin, and CK-MB may improve patient outcomes and conserve hospital resources compared with laboratory-based testing are examined in detail. Measurements of troponin, myoglobin, and CK-MB are useful in emergency care settings. Point-of-care tests are easy to perform and provide results rapidly enough to permit the use of marker concentrations in diagnosis and risk stratification. They offer an opportunity for clinicians to initiate prompt and aggressive treatments only when necessary, thus conserving hospital resources.
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