OBJECTIVE: Elevations of serum troponin T and I values are being used to diagnose acute myocardial infarction (AMI) and to rule out the condition in patients before their discharge from the emergency department (ED). However, the sensitivity and specificity of these tests vary considerably. Our goal was to systematically review the data on the accuracy of troponin T and I for the diagnosis of AMI in the ED.
SEARCH STRATEGY: We searched the MEDLINE database using the following strategy: troponin (text word) and diagnosis (medical subject heading [MeSH]) or troponin/diagnostic use (MeSH). The references of articles meeting our inclusion criteria were searched for a dditional articles.
SELECTION CRITERIA: We evaluated each study for quality. Only prospective blinded cohort studies with an adequate reference standard were included in the analysis.
DATA COLLECTION/ANALYSIS: Data from each study were abstracted by 2 investigators. We graphed sensitivity and specificity for different points in time from arrival in the ED or from the onset of pain and calculated summary estimates when appropriate and possible.
MAIN RESULTS: Sensitivity increases for both troponin T and I from 10% to 45% within 1 hour of the onset of pain (depending on the cutoff) to more than 90% at 8 or more hours. Specificity declines gradually from 87% to 80% from 1 to 12 hours after the onset of chest pain for troponin T and is approximately 95% for troponin I. The peak abnormal value in the first 24 hours after admission to the ED has an area under the receiver operating characteristic curve of 0.99 and is very useful at ruling out AMI if negative.
CONCLUSIONS: Although troponin T and I values are useful tools for the diagnosis of AMI, they must be interpreted according to the number of hours from the onset of chest pain. The test is particularly useful at ruling out MI when the value is negative at 8 or more hours after the onset of chest pain.
Clinical question
How accurate are troponin T and I values for the diagnosis of acute myocardial infarction in adult patients presenting to the emergency department?
Until recently, creatine kinase (CK) and creatine kinase, myocardial bound (CK-MB) fractions were used most often for evaluating patients with acute chest pain and suspected acute myocardial infarction (AMI). The World Health Organization (WHO) criteria for diagnosing AMI include elevation in this blood test result, along with typical electrocardiographic changes and a history compatible with ischemia.1 Recently, elevations in the serum troponin T and troponin I levels have been used both to test for AMI and to predict adverse cardiac events.2
However, interpretation of the troponin test results can be problematic. The test characteristics vary considerably, depending on the cutoff used to define abnormal, the troponin fraction used (T or I), and the time from the onset of myocardial ischemia. For example, increases in the cutoff number will decrease sensitivity but improve specificity.3 Because the troponin tests rely on damage to myocardial cells and the release of troponins into the circulation, sensitivity initially increases with the number of hours from the onset of chest pain, then decreases as the enzyme is cleared from the circulation. However, many of the reports on which current estimates of sensitivity and specificity are based do not report the time from the onset of symptoms or only provide the worst value in the first 24 hours. Decision making in the emergency department (ED) is often based on earlier values, and it is therefore important to carefully describe the accuracy of the test at different times.2
One previous meta-analysis of the use of troponins for diagnosing AMI was published.4 Unfortunately, it had several limitations. The literature review was abbreviated, and numerous important articles have been published since the review was completed. There was no assessment of study quality, and the outcome used was adverse cardiac events rather than diagnosis of AMI. We report the results of a systematic review of the literature documenting use of troponins for diagnosing AMI, with assessment of the quality of the studies and synthesis of results when appropriate.
Methods
Search Strategy
We conducted a search of the MEDLINE database in June 1999 using the following strategy: troponin (text word) and diagnosis (medical subject heading [MeSH]) or troponin/diagnostic use (MeSH). This initial search identified approximately 800 articles. The abstract of each article was reviewed, and articles were evaluated in detail if: (1) troponins were used in the diagnosis of heart disease; (2) the study involved human subjects; and (3) the articles were written in English, German, French, or Spanish. A total of 114 articles met these basic criteria. A second search of the 1999 literature took place in December 1999, and 10 additional articles that met the basic criteria were identified.