Abstract: Objective　To investigate the relationship between myeloperoxidase（MPO）concentration and the onset and progression of acute coronary syndrome（ACS）and the clinical significance of MPO in patients with chest pain.   Methods　A total of 78 patients with chest pain were enrolled and classified into 41 patients with ACS，17 patients with stable angina pectoris（SAP）and 20 controls according to the guideline of American College of Cardiology(ACC)/ American Heart Association（AHA). MPO concentration was measured by enzyme-linked immunosorbent assay. White blood cell（WBC)，neutrophil（Neu），red blood cell（RBC)，platelet（PLT)，total cholesterol（TC)，low-density lipoprotein cholesterol（LDL-C)，high-density lipoprotein cholesterol（HDL-C)，triglyceride（TG)，creatine kinase MB isoenzyme（CK-MB)，aspartate aminotransferase（AST)，fasting blood glucose（FBG)，lactate dehydrogenase（LDH）and high sensitive C reactive protein（hs-CRP）were detected. The correlations between MPO and other parameters were analyzed. By the receiver operating characteristic（ROC）curve，the area under ROC curve（AUC）was calculated. The diagnostic performance of MPO for ACS was evaluated. This technology was compared with the diagnostic methods of clinical manifestation analysis and coronary angiography based on the measurement of Kappa concordance. Results　The plasma MPO concentration in patients with ACS was significantly higher than those in patients with SAP and controls （P＜0.05），and the MPO concentration in patients with SAP was higher than that in controls （P＜0.05). The positive correlation was observed between MPO concentration and Neu，CK-MB and the severity of disease （r＝0.288，0.469 and 0.757，P＝0.018，0.043 and 0.000). MPO concentration did not correlate with age，hs-CRP，TC，LDL-C，HDL-C，TG，AST，FBG，LDH，RBC and PLT （P＞0.05). The cut-off value for MPO was identified as 212.59 μg/L（AUC＝0.927，P＝0.000）. In 41 patients with ACS，39 cases were MPO positive，and 2 cases were MPO negative. In 37 non-ACS patients（17 patients with SAP and 20 controls)，5 cases were MPO positive，and 32 cases were MPO negative. The sensitivity was 95.1%，the specificity was 86.5%，and the total concordance rate was 91.0%. The false negative rate（missed-diagnosis rate）was 4.9%，and the false positive rate（misdiagnosis rate）was 13.5%. The positive and negative predictive values were 88.6% and 94.1%. The Kappa value was 0.819（P＝0.000)，and the concordance of the 2 methods was good. Conclusions　MPO is a novel marker of inflammation for the diagnosis of ACS and has an important clinical significance for the identification of ACS.

Key words: Myeloperoxidase, Acute coronary syndrome, Chest pain, Inflammation marker