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Objective To evaluate how selection of patients for high sensitivity cardiac troponin testing affects the diagnosis of myocardial infarction across different healthcare settings. Design Prospective study of three independent consecutive patient populations presenting to emergency departments. Setting Secondary and tertiary care hospitals in the United Kingdom and United States. Participants High sensitivity cardiac troponin I concentrations were measured in 8500 consecutive patients presenting to emergency departments: unselected patients in the UK (n=1054) and two selected populations of patients in whom troponin testing was requested by the attending clinician in the UK (n=5815) and the US (n=1631). The final diagnosis of type 1 or type 2 myocardial infarction or myocardial injury was independently adjudicated. Main outcome measures Positive predictive value of an elevated cardiac troponin concentration for a diagnosis of type 1 myocardial infarction. Results Cardiac troponin concentrations were elevated in 13.7% (144/1054) of unselected patients, with a prevalence of 1.6% (17/1054) for type 1 myocardial infarction and a positive predictive value of 11.8% (95% confidence interval 7.0% to 18.2%). In selected patients, in whom troponin testing was guided by the attending clinician, the prevalence and positive predictive value were 14.5% (843/5815) and 59.7% (57.0% to 62.2%) in the UK and 4.2% (68/1631) and 16.4% (13.0% to 20.3%) in the US. Across both selected patient populations, the positive predictive value was highest in patients with chest pain, with ischaemia on the electrocardiogram, and with a history of ischaemic heart disease. Conclusions When high sensitivity cardiac troponin testing is performed widely or without previous clinical assessment, elevated troponin concentrations are common and predominantly reflect myocardial injury rather than myocardial infarction. These observations highlight how selection of patients for cardiac troponin testing varies across healthcare settings and markedly influences the positive predictive value for a diagnosis of myocardial infarction.

Background Cardiac troponin is integral to the diagnosis of myocardial infarction, but is elevated in many patients without acute coronary syndrome. We evaluate the impact of a clinical assessment of pre-test probability on the positive predictive value (PPV) of cardiac troponin for a diagnosis of myocardial infarction. Methods In 1,054 consecutive patients undergoing blood sampling in the Emergency Department, cardiac troponin I was measured in excess serum using a high-sensitivity assay. Patients were classified as type 1 or type 2 myocardial infarction, or myocardial injury, and the prevalence determined in the entire cohort and in those where testing was requested by the attending physician. We determine the predicted PPV for type 1 myocardial infarction across different pre-test probabilities. Results Cardiac troponin was requested in 136 patients identifying 15 (11.3%) with type 1 myocardial infarction. Testing everyone identified 2 further patients with type 1 (17/1,054 [1.7%]), but 127 (12%) patients with type 2 myocardial infarction or myocardial injury. In patients selected for testing the PPV for type 1 myocardial infarction was 50.0% (95% confidence interval [CI] 32.8%-67.2%), falling to 13.6% (95% CI 8.0%-19.7%) when measured across the cohort. The PPV was heavily influenced by the pre-test probability (Figure 1). Irrespective of diagnosis, cardiac troponin was a independent predictor of death (hazard ratio 1.26 per 2-fold increase, 95% CI 1.06 to 1.49) (Figure 2). Conclusions Cardiac troponin concentrations are elevated in one in eight patients in the Emergency Department. If testing is performed without an assessment of pre-test probability, interpretation of cardiac troponin will be challenging and may adversely impact on the diagnosis of acute myocardial infarction.