Overview

Kidney problems can develop suddenly (acute) or over the long term (chronic). Many conditions, diseases, and medicines can create situations that lead to acute and chronic kidney problems. Acute kidney injury, which used to be called acute renal failure, is more commonly reversible than chronic kidney failure.

• Acute kidney injury (AKI) is usually caused by an event that leads to kidney malfunction. Common causes include serious infection, blood loss from major surgery or injury, or the use of some medicines.
• 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 kidney injury 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 kidney injury, 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 very little kidney function remains. Other problems may develop with chronic kidney disease, such as anemia and increased levels of phosphorus 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 kidney injury occur in people who are already in the hospital for other reasons. In these people, acute kidney injury 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 points to a decrease in kidney function. Your doctor will compare these levels to previous tests to find out if your kidney problem 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.