Contrast-induced nephropathy (CIN) is a frequent and serious complication in ST-elevation myocardial infarction (STEMI) patients undergoing percutaneous coronary intervention (PCI).However,there is no consensus on the best definition of CIN in order to identify patients at risk.Methods In this retrospective,observational study,all patients with STEMI referred for PCI were included.The relationship between different CIN definitions and adverse events were analyzed.Results Totally 492 patients were enrolled.The incidence rate of CIN varied according to different definitions:10.4％ when defined as an absolute increase in SCr ≥0.5 mg/dL while 24.2％ as elevation of SCr by 25％.In-hospital MACEs rate was significantly higher in SCr ≥0.5 mg/dL (54.9％ vs.31.3％,P=0.003).Multivariate analysis showed that CIN defined as an absolute increase of SCr≥0.5 mg/dL (OR=5.03,P＜0.001) or elevations of SCr by 25％ (OR=2.71,P=0.003) was a strong significant predictor of in-hospital MACEs.Kaplan-Meier analysis showed that cumulative long-term survival rate was significantly lower in patients with an absolute increase in SCr ≥0.5 mg/dL (Log-rank=60.84,P＜0.001) or elevation of SCr by 25％ (Log-rank=15.66,P＜0.001).Conclusion CIN is a frequent and serious complication of STEMI treated by PCI.The definition by absolute increase of SCr ≥0.5 mg/dL is better in identifying patients with CIN at high risk of poor outcomes.