Hypothesis: In patients that present to an urban emergency room, a single urine neutrophil gelatinase-associated lipocalin (NGAL) measurement can classify their kidney disease as stable chronic kidney disease, acute tubular necrosis, urinary outlet obstruction or pre-renal azotemia.

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.

Inclusion Criteria:

A. Must be greater than or equal to 18 years of age

B. Must satisfy the following age and sex stratified serum creatinine levels:

1. men between ages 18 and 50 with serum creatinine greater than 1.2mg/dl
2. women between ages 18 and 50 with serum creatinine greater than 1.2mg/dl
3. men older than 50 with serum creatinine greater than 1.0mg/dl
4. women older than 50 with serum creatinine greater than 0.8mg/dl

C. All pts greater than or equal to 18 years of age without kidney failure defined by B

Patients admitted to the hospital through the emergency room who meet the inclusion / exclusion criteria for this study.