Background: Creatinine clearance (CCr) and Hemoglobin (Hb) is readily-available routine laboratory test that can predict clinical outcomes in patients with acute coronary syndrome. The aim of this study was to evaluate the impact of a CCr and Hb composite index (CHI) on long-term clinical outcomes in patients with ST-segment elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PCI) with drug-eluting stents. Methods: We analyzed consecutive 326 STEMI patients treated with primary PCI within 12 hours of onset of symptom. Cox regression analysis determined the optimal combination of CCr and Hb into a CHI. The discriminative ability of CHI, CCr and Hb in predicting 12-month major adverse cardiovascular events (MACE), composite of all cause of death, nonfatal MI and ischemic stroke were compared using area under the receiving operating characteristic curve. Results: The optimal weighting of CCR and Hb to form a CHI to predict 12-month MACE was Hb + CCr/12. The area under the curve for CHI was significantly greater (0.857) than for Hb (0.777, p=0.003) and CCr (0.802, p=0.039). A positive trend between MACE and CHI quintiles was observed; 39.4%, 9.4%, 6.1%, 0.0%, 1.5% of MACE occurred from quintiles 1 to 5 (p <0.001). In a multivariable setting, patients with first quintile (Q1 vs. Q5) showed the highest 12-month MACE risk (HR: 26.77, 95% CI 2.86-250.66, p=0.004) after adjusting for standard risk factors. MACE-free survival rate was significantly lower in patients with first quintile compared to patients with other quintiles (p <0.001) (Figure) Conclusion: The CHI is a useful and powerful marker to predict 12-month MACE in patients with STEMI who underwent primary PCI, with a superior discriminative ability than CCr or Hb.