Acute renal failure (ARF), also known as acute kidney injury, occurs when the kidneys fail to function, removing waste and balancing electrolytes in the blood. The three main causes are decreased blood flow, damage from medications/toxins, and blockages in the urinary tract from kidney stones or tumors. Symptoms include little urine, swelling, nausea, confusion and back pain below the ribs. Untreated ARF can be life-threatening as toxins build up in the body. Tests like BUN measure kidney function by detecting waste product urea in the blood. Extracorporeal shock wave lithotripsy and retrograde pyelograms are procedures used to treat and diagnose kidney stones.