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Bladder outlet obstruction

Alternative names

BOO; Lower urinary tract obstruction; Prostatism


This obstruction is at the base of the bladder, and it reduces or prevents the flow of urine into the urethra (the tube that carries urine out of the body).

Causes, incidence, and risk factors

Bladder outlet obstruction can have many different causes. Some of the most common causes of BOO include:

  • Benign prostatic hyperplasia (BPH)
  • Bladder calculi (stones)
  • Urethral stricture (scar tissue)
  • Bladder tumors (cancer)
  • Pelvic tumors (cervix, prostate, uterus, rectal)

Less common causes of bladder outlet obstruction include:

  • Cystocele
  • Posterior urethral valves (congenital birth defect)
  • Foreign objects
  • Urethral spasms
  • Urethral diverticula

Bladder outlet obstruction is most common in the aging male. Bladder stones and bladder cancer are also more commonly seen in men than women. As men age, their chances of developing these diseases increases dramatically. One in three American males over the age of 60 has significant symptoms of bladder outlet obstruction.

Related topics:
  • Bladder stones
  • Obstructive nephropathy
  • Reflux nephropathy
  • Benign prostatic hypertrophy


The symptoms of bladder outlet obstruction may vary. The most common symptoms experienced include:

  • Slow urinary flow
  • Delayed onset of urination (urinary hesitancy)
  • Inability to urinate (acute urinary retention)
  • Urinary stream starts and stops (urinary intermittency)
  • Urinary tract infection
  • Abdominal pain
  • Pain on urination (dysuria)
  • Frequent urination
  • Continuous feeling of a full bladder

Signs and tests

If bladder outlet obstruction is suspected, your health care provider will take a thorough history of your problems and perform a physical exam. On physical exam, your health care provider may find one or more causes of bladder outlet obstruction which include:

  • A distended bladder
  • A large prostate (men)
  • A cystocele (women)
  • Abdominal mass

In addition to a physical exam your health care provider may order a variety of tests which may include:

  • Serum chemistries to determine if kidney damage is being done
  • Ultrasound to determine where the blockage of urine is, and how well you can empty your bladder
  • IVP to determine where the blockage of urine is
  • Urinalysis to determine if blood or infection is present
  • Urine culture to determine if an infection is present
  • Uroflow to determine how fast the urine flows out
  • Urodynamic testing is a more sophisticated way of determining how well the bladder contracts and how blocked the flow of urine is


Treatment of bladder outlet obstruction depends on the underlying cause of the obstruction. For most cases, a Foley catheter (a catheter through the urethra into the bladder) is able to relieve the obstruction temporarily.

Occasionally, a suprapubic catheter (a catheter through the abdomen into the bladder) is needed to drain the bladder.

Long-term treatment of bladder outlet obstruction is mostly surgical. However, medical treatment options are available for many of the diseases that cause BOO. You should have a thorough discussion of treatment options with your health care provider.

Expectations (prognosis)

If diagnosed early, most causes of BOO can be treated with great intended effects. However, if diagnosis is delayed, permanent damage can result.


Complications of BOO can be devastating. Permanent damage can be done on all parts of the urinary system with long term and/or high-grade bladder outlet obstruction.

Complications of BOO include:

  • Renal failure
  • Recurrent urinary tract infection
  • Urinary incontinence
  • Urinary retention
  • Bladder and renal calculi

Calling your health care provider

If you feel that you have signs or symptoms of bladder outlet obstruction, call your health care provider. Early diagnosis is important and can often lead to a simple and effective cure.


Prevention of BOO is achieved by preventing the underlying cause of obstruction.

Update Date: 5/25/2002

Young Kang, M.D., Department of Urology, Columbia University College of Physicians and Surgeons, New York, NY. Review provided by VeriMed Healthcare Network.

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Last updated: Tue, 06 Jan 2009 00:20:03 GMT