Identification and Validation of Biomarkers of Acute Kidney Injury Recovery

Inclusion Criteria:a. * Males and females 21 years of age or older * Receiving care in an intensive care unit * Expected to remain in the ICU for at least 48 hours after enrollment * Use of indwelling urinary catheter as standard care at the time of enrollment * Subject must have acute kidney injury (KDIGO stage 2 or stage 3) at the time of the first sample collection * First sample must be collected within 36 hours of meeting KDIGO stage 2 criteria * Written informed consent provided by patient or legally authorized representative (LAR) Exclusion Criteria: * Prior kidney transplantation * Comfort-measures-only status * Already receiving dialysis (either acute or chronic) or in imminent need of dialysis at the time of enrollment * History of human immunodeficiency virus (HIV) or hepatitis virus (based upon available medical records) infections (NOTE: HIV or hepatitis testing need not be performed for enrollment in this study.) * Special populations, pregnant women, prisoners or institutionalized individuals * Patient meets any of the following: * Active bleeding with an anticipated need for \> 4 units PRBC in a day * Hemoglobin \< 7 g/dL * Any other condition that in the physician's opinion would contraindicate drawing serial blood samples for clinical study purposes