LCN2 and acute kidney injury: To find out the incidence and risk factors of AKI in post cardiac surgery patients in our hospital, to assess the ability of urinary NGAL and IL-18 in the early detection of AKI, to differentiate of pre-renal from intrinsic AKI and to predict the severity of AKI as per the “Risk, Injury, Failure, Loss, End stage”, [RIFLE] criteria.