Postrenal Acute Kidney Injury

Topic Overview

Postrenal acute kidney injury, which used to be called acute renal failure, occurs when an obstruction in the urinary tract below the kidneys causes waste to build up in the kidneys. It is not as common as intrinsic acute kidney injury (AKI) or acute tubular necrosis (ATN).

A blockage in the urinary tract may cause urine to build up in one or both kidneys. Over time, this fluid buildup can prevent the normal flow of urine out of the kidney. Conditions that may lead to postrenal acute kidney injury include:

• Kidney stones. Kidney stones most often develop in the ureters. They may also develop in the urethra.
• An enlarged prostate (benign prostatic hyperplasia, or BPH). An enlarged prostate gland may put pressure on the urethra, causing urine to back up in the bladder.
• A bladder that doesn't empty properly. This may be caused by certain nervous system disorders, such as stroke, multiple sclerosis, spinal cord injury, or Parkinson's disease.
• Blood clots in the ureters or urethra.
• Cancer of the prostate, cervix, or colon.

Postrenal acute kidney injury requires immediate treatment. When detected early, it usually can be reversed by removing or bypassing the obstruction in the urinary tract, before any permanent damage to the kidneys occurs.

• If the blockage is a kidney stone, your doctor can remove or destroy the stone. The most commonly used medical procedure for kidney stones is extracorporeal shock wave lithotripsy. This treatment uses sound waves that pass easily through the body but are strong enough to break up a kidney stone.
• For a blockage that cannot be removed, your doctor can use a catheter or a stent to reroute the urine flow around the blockage. Placing a catheter in the bladder to empty it may relieve symptoms and allow kidney function to return to normal.

Most people regain normal kidney function if the condition is reversed promptly.

If the obstruction is not relieved, the waste buildup and pressure on the kidneys may damage kidney tissue. Acute kidney injury is much harder to reverse after damage to the kidneys has occurred.