Introduction The Universal Definition recommends the 99 percentile of cardiac troponin as the diagnostic threshold for myocardial infarction (MI) in patients with suspected acute coronary syndrome if the assay achieves a coefficient of variation (CV) <10%. However, due to imprecision in contemporary assays and concern of over diagnosing myocardial infarction, diagnostic thresholds are currently set at higher concentrations where the assay can achieve CV ≤10%. The aim of this study was to assess the relationship between plasma troponin I concentrations, assay precision and clinical outcomes in patients with suspected acute coronary syndrome.
Methods Using a contemporary sensitive troponin I assay, consecutive patients admitted with suspected acute coronary syndrome (n=2092) were stratified according to the 99th percentile (0.012 ng/ml; CV 20.8%) and current diagnostic threshold (0.05 ng/ml; CV 7.2%) into three groups: <0.012 ng/ml, 0.012–0.049 ng/ml and ≥0.05 ng/ml. Event-free survival (recurrent myocardial infarction or death) at 1 year was compared between patients grouped by troponin I concentration.
Results Plasma troponin concentrations were <0.012 ng/ml in 988 patients (47%), 0.012–0.049 ng/ml in 352 patients (17%) and ≥0.05 ng/ml in 752 patients (36%). At 1 year, patients with troponin concentrations 0.012–0.049 ng/ml were more likely to be dead or readmitted with recurrent myocardial infarction compared to those with troponin concentrations <0.012 ng/ml (13% vs 3%; OR 4.8, 95% CI 3.0 to 7.7; p<0.001). Compared to troponin ≥0.050 ng/ml, patients with troponin 0.012–0.049 ng/ml had a higher risk profile but were less likely to be diagnosed with, or investigated and treated for, acute coronary syndrome.
Conclusions Lowering the diagnostic threshold to the 99th percentile and accepting greater assay imprecision would identify those at high-risk of recurrent MI and death, but increase the diagnosis of MI by 46%. It remains to be established whether reclassifying and treating these patients as MI would improve outcome.
- Myocardial infarction
- cardiac troponin
- universal definition