A Systematic Review of Troponin T and I Values as a Prognostic Tool for Patients with Chest Pain

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Original Research

A Systematic Review of Troponin T and I Values as a Prognostic Tool for Patients with Chest Pain

J Fam Pract. 2000 August;49(8):746-753

By

Mark H. Ebell, MD, MS

References

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CLINICAL QUESTION: How accurate are troponin T and I values for determining the prognosis of patients presenting with acute chest pain syndromes?

OBJECTIVE: The accuracy of the troponin T and I test as a prognostic tool for patients with chest pain varies considerably depending on the patient population, the cutoff for an abnormal test result, and other factors. The goal of our systematic review was to synthesize the best available evidence on this topic.

SEARCH STRATEGY: We searched the MEDLINE database, bibliographies of identified articles, and articles identified from a previous meta-analysis of diagnosis.

SELECTION CRITERIA: We included cohort studies that had at least 80% follow-up and reported useful data.

DATA COLLECTION AND ANALYSIS: Data from each study were abstracted by 2 investigators. We calculated sensitivity and specificity for the prediction of death, fatal or nonfatal myocardial infarction (MI), or any cardiac event for each combination of patient population, troponin test, interval from admission to blood draw, and cutoff for an abnormal test result.

MAIN RESULTS: For patients with chest pain and a normal electrocardiogram, the peak troponin I level drawn 6 or more hours after the onset of chest pain is useful for identifying patients at low risk of death or nonfatal MI at 30 days (negative likelihood ratio=0.07; probability of outcome=0.3% with a negative test, given a pretest probability of 4.4%). For patients with unstable angina, the sensitivity of troponin I for the identification of patients who die or have a nonfatal MI in the next 30 days is only 59%, and the specificity is only 79%. The sensitivity and specificity varied widely for patients with unstable angina or non-Q-wave MI depending on the inclusion criteria, cutoff used, timing of the blood draw, duration of follow-up, and other factors.

CONCLUSIONS: If the peak troponin T or I level measured at least 6 hours after the onset of chest pain symptoms is in the normal range in a patient with a normal electrocardiogram, it is very unlikely that the patient will die or have a nonfatal MI in the next 30 days (1%). The initial troponin value is not as helpful as the peak value at least 6 hours after the onset of chest pain. An abnormal troponin test result for patients with unstable angina or non-Q-wave MI identifies a subset at greater risk of death.

Not all patients with acute chest pain can be monitored as inpatients. Some are sent home with instructions to follow up with their personal physician, while others have noninvasive cardiovascular testing scheduled as outpatients. Formal protocols that use the history, physical examination, laboratory tests, or noninvasive testing have been developed and shown to reduce costs and improve outcomes.^1-4

Recently, it has been suggested that troponin T and I values may be useful for prognosis in patients with acute chest pain in the emergency department.^5,6 These enzymes are released by damaged cardiac muscle. However, the accuracy of troponin levels for the diagnosis of acute myocardial infarction (MI) varies considerably, depending on the specific test used, cutoff to define an abnormal test result, and timing of the blood test in relation to the onset of chest pain.⁷ The usefulness of these tests for prognosis is likely to be affected by the same factors.

The authors of several previous meta-analyses have considered this question. However, all of these studies had significant limitations. Wu and colleagues⁵ published a meta-analysis in 1995 that obviously could not include the large number of studies published since that time. The meta-analysis by Ollatidoye and colleagues⁶ included more studies but did not distinguish between different cutoffs to define an abnormal test result, combined all intervals from 4 days to 1095 days into a single summary estimate, and did not consider the time at which the troponin test was drawn in relation to either emergency department arrival or the onset of chest pain. In our study, we systematically reviewed the evidence for the accuracy of troponin T and I values in determining the prognosis of patients presenting to the emergency department with chest pain, unstable angina, and other acute coronary syndromes.

Methods

Search Strategy

We conducted searches of the MEDLINE database in June 1999 and December 1999 (the second search was of 1999 only). We used the following search strategy: troponin [text word] or troponin [MeSH] and prognosis [MeSH]. Studies were limited to those that provided an abstract, were written in English or German, and used human subjects. The October through December 1999 issues of the American Journal of Cardiology, the Journal of the American College of Cardiology, the American Heart Journal, and Clinical Chemistry were hand-searched. We also reviewed the bibliographies of articles meeting the final inclusion criteria. The abstract of each article was reviewed by one of the investigators, and articles were evaluated in detail if troponin levels were used to predict the prognosis of patients with chest pain, unstable angina, or other acute coronary syndromes.