Inclusion Criteria:  Patients undergoing cardiac surgery were prospectively enrolled.  Exclusion Criteria:  History of End Stage Renal Disease or on Dialysis; prior kidney transplantation; patients with a DNR order; pregnancy; moribund patients with expected death within 24 h or whose survival to 28 days was unlikely due to an uncontrollable comorbidity (i.e., end-stage liver or heart disease, untreatable malignancy)