Limitations
An important limitation of any systematic review of this topic is the wide variety of cutoffs, manufacturers, processes, and reagents used in the studies. Ideally, each clinical site will identify for its physicians the optimal cutoffs for each test at each point in time. This is probably unrealistic, however, and we hope our results will guide physicians in the absence of such data. Although differences in the manufacturing of a particular test may affect the sensitivity and specificity, there was no clear pattern in these data, and other differences between study populations, settings, and inclusion criteria made it difficult to quantify the magnitude of this effect.
The diagnosis of AMI is only one use of troponin and other biochemical markers. Risk stratification is another important goal, and a future systematic review will evaluate the ability of troponin T and I to stratify patients into high-risk and low-risk groups for adverse cardiac events.
Recommendations for future research
Although an important goal of systematic reviews is to provide summary estimates of the accuracy of diagnostic tests, it is equally important to use these results to guide further research. Because the sensitivity of troponin T and I is so dependent on the number of hours from the onset of chest pain, future studies should always record this time when the blood is drawn. Using time from the admission to the ED is less useful, because pain could have begun any time before arrival. Also, the investigators of future studies should use the WHO criteria for AMI, ensure blinding of the diagnosing physicians to the results of the troponin test, and provide adequate data for future systematic reviews and meta-analyses. Finally, studies should measure troponin T and I, myoglobin, and CK so their accuracy can be compared for both diagnosis and prognosis.
Recommendations for clinical practice
Although troponin T and I are useful for the diagnosis of AMI, clinicians should interpret the results according to the number of hours from the onset of chest pain, whenever possible. Table 2 and the nomograms on the Journal’s Web site (www.jfampract.com) can assist in this task. A peak value of troponin T of less than 0.2 in the first 24 hours after arrival in the ED is strong evidence against the presence of AMI; a normal troponin T or I value from blood drawn 8 or more hours after the onset of chest pain is also strong evidence against its presence. However, a normal value of troponin T or I at the time of admission or within 4 or fewer hours of the onset of pain does not significantly reduce the likelihood of AMI. Abnormal values of troponin T or I from blood drawn 8 or more hours after the onset of chest pain are moderately strong evidence in favor of the presence of AMI, particularly for patients who are otherwise at high risk.
Acknowledgments
This work was supported by the Michigan Consortium for Family Practice Research, one of 3 research centers funded by the American Academy of Family Physicians and its members. The authors do not have any financial or professional connection to the manufacturer of any test kits. We wish to thank Ian Katz, MD; Alan Wu, MD; Johannes Mair, MD; Hugo Katus, MD; and Bernd Puschendorff, MD, for their willingness to share their original data for this systematic review. We also wish to thank Deb Richardson for her assistance with the preparation of this manuscript.