Objective To prospectively evaluate the value of cystatin C (CysC) in diagnosis of contrast-induced acute kidney injury (CIAKI) among patients undergoing Percutaneous Cardiovascular Intervention (PCI).Methods Patients who underwent PCI procedures in our hospital were enrolled.Serum creatinine(SCr) and CysC were measured at baseline before,24 h and 48 h after PCI,respectively.CysC were examined by particle-enhanced turbidimetric immunoassay (PETIA).CIAKI was defined as a relative increase in SCr concentration of at least 25％ or an absolute increase more than 44.8 mmol/L (0.5 mg/dl) within 48 h in the absence of other related causes.Results Among 196 patients,135 were male and 61 female with a mean age of(70.4 ± 11.3)years old.Twenty-nine (14.8％)patients developed CIAKI according to the SCr criteria.The area under the ROC curve (AUC) at 24 h and 48 h post PCI were 0.661 (95％ CI 0.548-0.774,P =0.006) and 0.783 (95％ CI 0.701-0.865,P ＜ 0.001),respectively.The diagnostic sensitivities of CysC at 24 h and 48 h were between 6.9％ and 48.28％,while,the diagnostic specificities and negative predictive values of CysC were between 85.03％-97.60％ and 85.79％-90.45％,respectively.The 15％ elevation of 48 h CysC yielded the diagnostic sensitivity of 41.38％,specificity of 92.86％,negative predictive value of 90.17％,corrective rate of 85.28％ with Youden Index of 0.342 4.Conclusions In this study,CysC presented an excellent diagnostic specificity and negative predictive value in diagnosis of CIAKI.It might be used as a tool for excluding CIAKI in clinical practice.48 h CysC performed better than 24 h CysC in CIAKI diagnosis,among which a 15％ increment achieved relatively the best diagnostic value.