Substantial basic and translational research has been directed to detect earlier and more sensitive acute kidney injury (AKI) biomarkers over the past decade. Much of the seminal AKI biomarker validation research has been performed in children undergoing cardiopulmonary bypass since they represent an ideal clinical model for AKI biomarker study: the timing of the injury is known and children do not have many of the co-morbidities seen in adult patient populations, which can confound the clinical situation. Ricci and colleagues report the results of their study using two novel urinary AKI biomarkers, neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C--not to predict AKI, but to define it--in a randomized trial of intraoperative fenoldopam to prevent AKI. They demonstrate that fenoldopam administration led to decreased postoperative urine NGAL and urine cystatin C concentrations, suggesting a renoprotective effect. Given the high sensitivity of NGAL for AKI post cardiopulmonary bypass, this study provides a model to use novel AKI biomarkers in a novel manner.