Urinary NGAL has been shown to be an early marker of AKI following paediatric cardiac surgery (2 hours off pump). Previous studies showed that an early increase of urinary NGAL following cardiopulmonary bypass was an excellent predictor for a later >50% increase in serum creatinine concentration in children undergoing cardiac surgery. Increased urinary concentrations of NGAL were found following open heart surgery. When defining AKI as an >50% increase of serum creatinine from baseline, the increase of urinary NGAL concentration two hours off pump appeared to be an excellent predictor of AKI. Several studies included heterogeneous populations of patients aged one month to 21 years undergoing cardiac surgery. Besides, NGAL concentrations have not been studied in neonates after open heart surgery, neither has been identified the threshold for accurate prediction of severe AKI requiring renal replacement therapy (RRT). If such a threshold was identified, urinary NGAL could be provided for intervention.