Background: Neutrophil Gelatinase Associated Lipocalin (NGAL) is a new biomarker which can predict acute kidney injury (AKI) in critically ill patients. Usefulness of NGAL in the early diagnosis of all types of AKI is under question. We hypothesized NGAL is an early predictive biomarker of contrast-induced nephropathy (CIN).
Methods: In this process evaluation study, we enrolled 122 patients (Mean age 59.7±10.8 years) undergoing elective angiography/angioplasty with contrast media during April to September 2009. Serial urine samples were analyzed in a double-blind fashion by NGAL enzyme-linked immunosorbent assay. CIN was defined as a 25% increase in baseline serum creatinine. 
Results : The prevalence of CIN was 30.3%. Significant elevations in urinary NGAL concentrations were noted within 12-h and 24-h after the procedure in patients with CIN. NGAL concentrations after 12 hours was 90.62±105.63 vs. 27.6±45.8 ng/ml in patients with and without CIN, respectively P=0.0001, and 79.78±117.7 vs. 30.92±52.84 ng/ml, 24 hours afterwards P=0.002. Some patients had AKI after five days of exposure rather than the second day (P=0.0001). We found using a cut-off point of 8 ng/ml with a sensitivity, specificity, negative predictive value and area under the ROC curve 94%, 25%, 91% and 0.75 respectively are good for the prediction of CIN in 12-h urinary NGAL and a cut-off point of 5.5 ng/ml with respective values of 97%, 24%, 95% and 0.70 for 24-h urinary NGAL.
Conclusion: Urine NGAL may represent a sensitive early biomarker of acute AKI after angiography/angioplasty. We recommend the routine measurement of NGAL in high risk patients receiving contrast agents.