摘要OBJECTIVE To determine the association of serum complement C1q levels with cardiovascular outcomes among patients with acute coronary syndrome (ACS) undergoing percutaneous coronary intervention (PCI), and evaluate the value of C1q modified by high-sensitivity C-reactive protein (hs-CRP) levels as an independent predictor. METHODS As a single-center prospective observational study, we analyzed 1701 patients who had received primary or elect-ive PCI for ACS at Beijing Anzhen Hospital, Capital Medical University, Beijing, China between June 1, 2016 and November 30, 2017. The associations of C1q modified by hs-CRP with major adverse cardiovascular events (MACE) were determined in survi-val analysis. RESULTS Patients with the lowest C1q tertile had the highest cumulative risk of MACE (log-rank P = 0.007). In fully adjusted Cox regression models, stratifying the total population according to hs-CRP dichotomy, C1q was significantly associated with MACE in patients with hs-CRP levels less than 2 mg/L but not in those with 2 mg/L or more (Pinteraction = 0.02). In patients with hs-CRP levels less than 2 mg/L, with the lowest C1q tertile as reference, the risk of MACE was reduced by 40.0％ in the middle C1q ter-tile [hazard ratio (HR) = 0.600, 95％ CI: 0.423–0.852, P = 0.004] and by 43.9％ in the highest C1q tertile (HR = 0.561, 95％ CI: 0.375–0.840, P = 0.005). CONCLUSIONS Serum complement C1q is significantly associated with cardiovascular outcomes in patients with ACS und-ergoing PCI, only when hs-CRP levels are less than 2 mg/L. This finding implicates the usefulness of C1q for the risk stratificat-ion in ACS patients with reduced systemic inflammation.