The purpose of this study is to determine whether urinary NGAL levels are able to distinguish the classical categories of renal disease. Previous studies have strongly suggested that this protein marks those with fulminant renal dysfunction with greater sensitivity and time resolution than currently used markers. Studies to date have been in highly selected populations: children and adults following cardiac surgery, infants with cardiovascular anomalies, and patients with known chronic kidney disease. Demonstration of similarly robust sensitivity and specificity in a broad Emergency Room population would strengthen the conception of NGAL as a marker of early or advancing kidney dysfunction. Most importantly, if NGAL can distinguish between types of renal disease at presentation in the ER, it might have important implications regarding ER management of these common presentations. For example, it could reduce diagnostic ambiguity and lag time from hours or days to seconds.