Cardiac troponin often falsely elevated in patients at low risk

Reference

Shah AS, Sandoval Y, Noaman A, et al. Patient selection for high sensitivity cardiac troponin testing and diagnosis of myocardial infarction: prospective cohort study. BMJ 2017;359:j4788.

Synopsis

To conduct this study, investigators enrolled consecutive patients drawn from 3 different groups. The first group consisted of every adult presenting to a United Kingdom emergency department for any reason for whom blood was drawn (n = 1054). This blood was used to determine their cardiac troponin level. The second and third groups comprised patients presenting to all emergency departments in the United Kingdom (n = 5815) and one emergency department in the United States (n = 1631) in whom high sensitivity troponin testing was requested by the attending clinician. To determine whether an MI occurred, 2 physicians independently reviewed all clinical information, including noninvasive and invasive investigations and outcomes occurring within 30 days of presentation. In the first group of unselected patients, cardiac troponin was elevated in approximately 1 in 8 patients (13.7%), though the prevalence of MI was only 1.6%. In patients specifically selected for troponin testing (presumably because they were symptomatic), the prevalence of MI was 14.5% in the United Kingdom but only 4.2% in the United States. For these patients the positive predictive value of an elevated troponin level was 59.7% in the United Kingdom but only 16.4% in the United States. The presence of all three indicators of MI—chest pain, ischemia on electrocardiography, and a history of ischemic heart disease—dramatically increased the positive predictive value of the test. A negative troponin test result in any of the populations effectively ruled out MI (negative predictive value 100%).