One-hundred and eighty-one patients (66.1%) were men; mean age was 68.2 ± 12.2 years. Valve replacement was performed in 123, coronary artery bypass graft (CABG) in 81, valve surgery + CABG in 48, cardiac transplant in five, aorta aneurism surgery in nine, and other procedures in eight patients. ICU and hospital stays were 6.7 ± 8.1 and 15.7 ± 13.9 days, respectively. Renal replacement therapy (RRT) was required in 16 patients (5.8%) within 48 hours of ICU stay and in 28 patients (10.2%) within 43weeks. Mortality at 28 days was 2.9%. Eighty-six patients (31.4%) were diagnosed with AKI within 48 hours of surgery. Area under the ROC curve of POST uNGAL for AKI diagnosis was 0.72 (0.66 to 0.79) (P 0.0001) at an optimal cutoff value of 1803 μg/l, with 78.7% specificity, 64% sensitivity and 74.1% accuracy. uNGAL advanced diagnosis of AKI in 44 patients (51.2%), whereas diagnosis was achieved at the same time as AKI criteria in 11 patients; AKI criteria outperformed uNGAL in only 36% of cases. Accordingly, uNGAL was useful to diagnose postoperative AKI in 63.9% of cases. Median delta uNGAL was 12.5 (from -1.9 to 71.1) and 154.5 (from 16.6 to 484.5) μg/l in non-AKI and AKI patients, respectively (P 0.0001) and its area under the ROC curve for AKI prediction was 0.70 (0.63 to 0.77) (P 0.0001).