Background Acute coronary syndrome (ACS) patients without troponin elevation were admitted with suspected non-ST-elevation acute coronary syndrome (NSTE-ACS) and have a heterogeneous prognosis.In contrast with troponin positive ACS patients these risk stratification remains obscure,because routine clinical parameters alone are not enough to stratify patients with suspected ACS.Many studies show that Monocyte subsets and monocyte-platelet aggregates (MPAs) play an important role in ACS.We sought to investigate whether or not there is an imbalance among the three monocyte subsets as well as their relative contribution to MPA formation in troponin negative NSTE-ACS patients,and explore their predictive values for discriminating between low risk and moderate-to-high risk troponin negative NSTE-ACS patients based on the Global Registry of Acute Coronary Events (GRACE) score.