Abstract： Background Contrast induced acute kidney injury (CIAKI) is an important complication in the use of iodinated contrast media (CM).Our study was to evaluate the neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C for early diagnosis of CIAKI.Methods The patients with established or suspected coronary artery disease (CAD) with the estimated glomerular filtration rate (eGFR) was more than 30 ml.min-1.1.73 m-2 and nor more than 90 ml·min-1·1.73 m-2 were continuously enrolled.The blood samples of the first 50 patients were obtained before and at 2,4,8,24 and 48 hours after procedure to identify the time points at which the biomarkers reached peaks and at which the blood samples of the rest of patients were obtained.The plasma NGAL and cystatin C measure used enzyme-linked immunosorbent assay (ELISA) kit.The diagnostic characteristics of absolute and relative increasing NGAL and cystatin C for CIAKI were evaluated.Results Total 311 patients were enrolled,among whom 39 (12.5％) developed CIAKI.Plasma NGAL increased at 2hours and reached peak at 4 hours after procedure,while plasma cystatin C increased at 2 hours and reached peak at 24hours after procedure.Thus,we determine rational point of time at 4 hours for NGAL and at 24 hours after procedure for cystatin C,respectively.The plasma NGAL at 4 hours after CM exposure showed largest area under curve (AUC) of 0.662 (95％ confidence interval (C/):0.565-0.758,P=0.002) with 51.5％ sensitivity and 80.6％ of specificity.The relative increasing 25％ of NGAL showed the best sensitivity and specificity of 0.872 and 0.808,respectively,with maximum Youden index of 0.680,while cystatin C with relative increasing more than 25％ had 76.9％ of sensitivity and 81.2％ of specificity.Combined two biomarkers might get more than 90％ of specificity.Conclusions Single measurement of NGAL or cystatin C had poor sensitivity and specificity; however,the relative increasing 25％ of NGAL at 4 hours after CM exposure demonstrated higher diagnostic values for CIAKI.Combining relative increasing plasma NGAL with relative increasing plasma cystatin C might perform better for early diagnosis of CIAKI.