Acute renal failure often does not cause symptoms that you notice. If you are already in the hospital, tests done for other problems may also detect your kidney failure. When symptoms do appear, they may include:

• Swelling, especially of the legs and feet.
• Little or no urine output.
• Thirst and a dry mouth.
• Rapid heart rate.
• Feeling dizzy when you stand up.
• Loss of appetite, nausea, and vomiting.
• Feeling confused, anxious and restless, or sleepy.
• Pain on one side of the back, just below the rib cage and above the waist (flank pain).

The symptoms can help your doctor find out what type of kidney failure is present.

• Severe dehydration, a common cause of prerenal acute renal failure, may cause extreme thirst, lightheadedness or faintness, and a weak, rapid pulse.
• A blockage in the urinary tract, which causes postrenal acute renal failure, may cause pain in the side or lower back, blood in the urine (hematuria), or reduced urine output (oliguria).

Uremic syndrome (uremia) is a serious complication of severe or prolonged acute renal failure. It can cause severe nausea, confusion, seizures, irregular heart rhythm, and fluid in the lungs ( pulmonary edema).