Serum complement C1q level is associated with acute coronary syndrome.

•Serum complement C1q in ACS patients, in particular AMI patients, showed lower level.•In non-smokers, serum complement C1q had a negative association with Gensini score.•The decreasing of serum complement C1q was an unfavorable factor for acute myocardial infarction.•Complement C1q may be related with the process of atherosclerosis and helpful to predict the severity of coronary disease.