Kidney failure occurs when the kidneys lose their ability to function. To treat kidney failure effectively, it is important to know whether kidney disease has developed suddenly (acute) or over the long term (chronic). Many conditions, diseases, and medications can create situations that lead to acute and chronic kidney disease. Acute renal failure is more commonly reversible than chronic kidney failure.

• Acute renal failure (ARF) is usually caused by an event that leads to kidney malfunction, such as dehydration, blood loss from major surgery or injury, or the use of medications, such as contrast agents used in X-ray tests, antibiotics such as gentamicin, or nonsteroidal anti-inflammatory drugs (NSAIDS) such as aspirin or ibuprofen.
• Chronic kidney disease (CKD) is usually caused by a long-term disease, such as high blood pressure or diabetes, that slowly damages the kidneys and reduces their function over time.

The presence or lack of symptoms may help your doctor determine whether acute renal failure or chronic kidney disease is present.

• Symptoms of decreased kidney function, such as fluid buildup or electrolyte imbalance, are more likely to develop with acute renal failure, regardless of how long the kidney has been malfunctioning. Symptoms may reflect the actual cause of the kidney problem.
  • An obstruction in the urinary tract may cause pain in the side or lower back (flank pain), blood in the urine, or reduced urine output.
  • Dehydration may cause extreme thirst; lightheadedness or faintness; a weak, rapid pulse; and other symptoms.
• Symptoms of chronic kidney disease may not develop until less than 10% to 15% of kidney function remains. Other problems may develop with chronic kidney disease, such as anemia and increased levels of phosphates in the blood (hyperphosphatemia), along with complications caused by kidney failure. These complications often do not develop until kidney disease has been present for some time.

Most cases of acute renal failure occur in people who are already in the hospital for other reasons. In these people, acute renal failure is usually diagnosed when routine tests show a sudden increase in creatinine and blood urea nitrogen (BUN) levels. A buildup of these waste products in the blood indicates a loss of kidney function. Your doctor will compare these levels to previous tests to determine if kidney disease is acute or chronic.

An ultrasound of the kidneys also may help determine whether kidney problems are acute or chronic. Normal-sized kidneys may be present in either condition, but when both kidneys are smaller than normal, chronic kidney disease is usually the problem.