Cardiac surgery associated acute kidney injury (CSA-AKI) is a potentially lethal complication which occurs in up to 30% of cardiac surgery patients. When the injury is severe enough to necessitate dialysis (which occurs in approximately 1% to 2% of patients) it confers a 19-fold increase in the odds of death. Even when the injury is relatively modest (i.e. a 25 % rise in postoperative serum creatinine), it is independently associated with morbidity and mortality. A major barrier to preventing CSA-AKI is the lack of available strategies for early detection of kidney injury. Work done by our team has established Hepcidin-25 as a novel urine biomarker of CSA-AKI. Newer data suggest NGAL, OSMR, MMP-2, and Klotho are also potential early biomarkers of CSAAKI. Objective: To study the value of 5 urine and serum biomarkers in the diagnosis of incipient CSA-AKI. A unique and novel aspect of our project will be assessing the value of intraoperative measurements of these biomarkers. Design: Prospective cohort study of 350 cardiac surgery patients (280 patients have already been recruited)