"Background Cardiac surgery–associated acute kidney injury (AKI) is an adverse outcome that increases patient morbidity and mortality. Serum creatinine as an early indicator of AKI has limitations because of its slow rise and poor predictive accuracy. This delay in diagnosis may lead to increased risk for adverse outcomes. Objective The study explored serum and urine activity of matrix metalloproteinases (MMPs)-2 and MMP-9 and their association, and earlier detection of AKI in patients following cardiopulmonary bypass (CPB)–supported surgery. We hypothesized that increased activity of serum and urine MMP-2 and/ or MMP-9 were associated with AKI. Furthermore, MMP-2 and/ or MMP-9 may provide earlier detection of AKI as compared with serum creatinine. Methods There were 150 CPB-supported surgeries, 21 of which developed AKI who were then propensity matched with 21 non-AKI patients. Primary outcomes variables were serum and urine activity of MMP-2 and MMP-9 drawn at specific intervals. Results At the 10-minute and 4-hour post-CPB time points, the serum MMP-2 activity of AKI patients was significantly higher as compared with non-AKI patients. At the same time post-CPB, the serum MMP-9 activity of AKI patients was significantly higher as compared with non-AKI patients. The activity of urine MMP-2 and MMP-9 of AKI patients was significantly higher as compared with non-AKI patients at all time points. Conclusion The data demonstrated that the serum and urine levels of activity of MMP-2, -9 are associated with the clinical endpoint of AKI and appear to have earlier rising levels as compared with serum creatinine."