This is the most serious form of kidney disease, if untreated, could lead to permanent kidney damage. Hospitalization is often required to find out the cause and immediate treatment. Tests including urine studies, blood test, kidney imaging and in some instances, kidney biopsy are required. Acute kidney injury can be a consequence of other systemic illnesses but can also arise from kidney itself. This is diagnosed by a blood test which checks BUN and creatinine, which are normally filtered and excreted in the urine by kidneys. Rapid rise in BUN and creatinine is seen in acute kidney injury. We often treat acute kidney injury in hospital. Mild form of acute kidney injury with obvious cause can be treated as an outpatient with close monitoring.