Individual parameters of complete blood count (CBC) have been associated with worse outcome in patients with acute coronary syndrome (ACS). However, the prognostic role of CBC taken as a whole has never been evaluated for long-term incidence of major adverse cardiovascular events (MACEs). Patients were grouped according to their hematopoietic cells’ inflammatory response at different time points during hospital stay. Patients with admission white blood cell count >10 × 10⁹/L, discharge hemoglobin <120 g/L, and discharge platelet count >250 × 10⁹/L were defined as “high-risk CBC.” Among 1076 patients with ACS discharged alive, 129 (12%) had a “high-risk CBC” and 947 (88%) had a “low-risk CBC.” Patients with “high-risk CBC” were older and had more comorbidities. Over a median follow-up of 665 days, they experienced a higher incidence of MACE compared to “low-risk CBC” patients (18.6% vs 8.1%). After adjustment for age, age-adjusted Charlson comorbidity index, female sex, cardiac arrest, suboptimal discharge therapy, coronary artery bypass, and ejection fraction, a high-risk CBC was significantly associated with increased MACE occurrence (adjusted hazard ratio 1.80; 95% CI: 1.09-3.00). The CBC was a prognostic marker in patients with ACS, and its evaluation at admission and discharge could better classify patient’s risk and improve therapeutic management.