Myeloperoxidase in the diagnosis of acute coronary syndromes: The importance of spectrum

Background Myeloperoxidase (MPO) is proposed for risk stratification in patients with suspected acute coronary syndromes (ACSs). We determined if MPO has diagnostic value in patients being evaluated for ACS. Method MIDAS was an 18-center prospective study enrolling suspected ACS emergency department patients who presented <8 hours after symptom onset and in whom serial cardiac markers and objective cardiac perfusion testing were planned. Blinded MPO (Biosite, Inc, San Diego, CA) and troponin I (Triage Cardio 3; Biosite, Inc) were drawn at arrival, and Troponin I (TnI) was measured at 90, 180, and 360 minutes. Final diagnoses were adjudicated by the local investigator blinded to study assay. Results Of 1,018 patients, 54% were male, 26% black, with a mean age of 58 +/- 13 years. Diagnoses were ACS in 288 (23%) and noncardiac chest pain (NCCP) in 788 (77%). Of patients with ACS, 94 (9.2%) had a myocardial infarction (MI) at presentation (69 non-ST-elevation MI, 25 ST-elevation MI), and 136 had unstable angina. Using a cutpoint of 210 ng/mL to provide 90% specificity, MPO had a sensitivity of 0.18; negative predictive value, 0.69; positive predictive value, 0.47; negative likelihood ratio, 0.91; and a positive likelihood ratio of 1.83 to differentiate ACS and NCCP. Because of the large overlap of quartiles, MPO was not clinically useful to predict serial TnI changes. The C statistics +/- 95% CI for MPO differentiating ACS from NCCP and for AMI versus NCCP were 0.629 +/- 0.04 and 0.666 +/- 0.06, respectively. Conclusions Myeloperoxidase has insufficient accuracy for decision making in patients with suspected ACS. (Am Heart J 2011;162:893-9.)