Acute kidney injury (AKI) is a common clinical event with severe consequences. In the pediatric intensive care unit (PICU), AKI occurs in almost 10% of all patients and evidence suggests that children are dying not just with AKI, but from AKI. Unfortunately, the treatment for AKI is limited to a great extent by delayed diagnosis. Reliance on markers of kidney injury that change only when significant damage has already occurred has rendered potential therapies ineffective. For this reason, identification of new markers of AKI that change early in the course of injury is paramount. While new AKI biomarkers have been identified, their performance in the general PICU population is variable. The investigators recently proposed the concept of 'renal angina' as a way to risk stratify patients in the ICU for AKI risk. In the AKI-CHERUB study, the investigators propose to study renal angina in PICU patients alone and in combination with urinary biomarkers for AKI prediction. The investigators hypothesize that renal angina will increase the predictive precision of urinary biomarkers for AKI.