A problem with assessing the utility of diagnostic or screening tools for AKI in the critically ill is the heterogeneity of pathological insults, and the unpredictable early clinical course. This leads to difficulties in identifying control groups, and in capturing the evolution of AKI. We propose investigating the use of these novel biomarkers and proteomic techniques in the more homogenous group of patients undergoing cardiopulmonary bypass. This carries with it the benefits of thorough pre-operative testing with stable baseline measurements and a clearly definable renal insult in the form of bypass time. Post-bypass renal failure requiring RRT is estimated to occur in 1.5-2% of coronary artery grafting cases, and around 5% of combined graft/valve replacement cases; however, there is a far higher incidence of AKI as measured by creatinine rise and/or oliguria.