Abstract： Objective To observe the level of circulating CD31 +/CD42b-endothelial microparticles in patients with ST-elevated myocardial infarction (STEMI),and discuss the correlation between CD31 +/CD42b-and traditional myocardial injury index.Methods A total of 22 healthy subjects and 44 patients with angiographically confirmed coronary atherosclerotic lesions collected from January 2010 to December 2010 were studied prospectively.The patients were divided into SAP (stable angina pectoris,Canadian Cardiovascular Society,CCS Ⅱ to Ⅲ ) group (n =22) and STEMI group (n =22).The level of circulating CD31 +/CD42b-endothelial microparticles was detected by flow cytometric device after admission; creatine kinase (CK) and its isoenzymes (CK-MB) were detected by using biochemical analyzer; C-reactive protein was determined by a highly sensitive latex-enhanced turbidimetric immunoassay with a low detection limit of 0.25 mg/dl (IMMAGE,Beckman Coulter; Reagent from Orion Diagn Co.Ltd.,Vantaa,Finland).Cardiac troponin I was measured by chemiluminescence immunoassay (ACCESS2 from Beckman Coulter).In 22 STEMI patients,blood sample was taken not only after admission but subsequently at 4-hour intervals during the first 48 hours.Peak levels of myocardial enzymes after injury ( creatine kinase,CK; creatine kinase MB isoenzyme,CK-MB; c troponins I,cTnI) and high sensitive C reactive protein (hs-CRP) values were determined.The correlation between circulating level of CD31 +/CD42b(-) and peak levels of myocardial biomarkers after injury were analyzed.Results The endothelial micro-particles were significantly higher in STEMI patients than those in either SAP group or normal group ( P ＜ 0.01 ),whereas there was no difference between the latter two groups.In STEMI patients studied in these cross sectional study,circulating CD31 +/CD42b-microparticles were positively correlated with peak level of myocardial biomarkers after injury.Moreover,the correlations between myocardial biomarkers after injury ( CK,CK-MB,cTnl and hs-CRP) and circulating CD31 +/CD42b-microparticles were r =0.489,P =0.021; r =0.501,P=0.018; r=0.491,P=0.02; r=0.612,P=0.002.Conclusions The level of circulating blood CD31 +/CD42b-endothelial micro-particle was expected to become a predictive marker in STEMI.