Aim To investigate circulating levels of endothelial microparticle(EMP) in the plasma of patients with acute coronary syndromes(ACS),and to explore correlations between circulating EMP count and conventional risk factors of cardiovascular disease(CVD).Methods A case-controlled study was conducted in 56 patients with ACS and 26 control subjects without coronary heart disease.Circulating levels of CD31bright/Annexin V+ EMP were measured by flow cytometric analysis.Results Plasma CD31bright/Annexin V+ EMP levels were significantly higher in patients with ACS than those in control subjects(P<0.01).However there was no significant difference in plasma CD31bright/Annexin V+ EMP counts between patients with AMI and those with UAP.Among all subjects,patients with type 2 diabetics had increased plasma CD31bright/Annexin V+ EMP as compared with patients without diabetics(P<0.05).On multivariate analysis,serum triglyceride level was the major independent factor related to plasma CD31bright/Annexin V+ EMP count(r=0.28,P<0.05).In patients with ACS,linear regression analysis showed a strong positive correlation between serum high sensitivity C-reactive protein level and plasma CD31bright/Annexin V+ EMP count(r=0.31,P<0.05).Conclusions Plasma CD31bright/Annexin V+ EMP increased in patients with ACS or diabetics,and plasma CD31bright/Annexin V+ EMP count was correlated with conventional risk factors for CVD.These findings suggest that the more critical endothelial damage is present in ACS patients and type 2 diabetics patients,increased level of plasma CD31bright/Annexin V+ EMP is relative with high concentration of plasma hs-CRP and triglyceride.