Bladder outlet obstruction

Alternative names
BOO; Lower urinary tract obstruction; Prostatism

Bladder outlet obstruction occurs at the base of the bladder, and 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 are:

  • 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 aging men, and is often caused by BPH. Bladder stones and bladder cancer are also more commonly seen in men than women. As a man ages, the chance of developing these diseases increases dramatically. One in three American males over the age of 60 has significant symptoms of bladder outlet obstruction.


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 provider may find one or more of the following possible causes:

  • Distended bladder  
  • Enlarged prostate (men)  
  • Cystocele (women)  
  • Abdominal mass

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

  • Serum chemistries to reveal kidney damage  
  • Ultrasound to locate the blockage of urine is, and find out completely the bladder is emptied  
  • IVP to locate the blockage is  
  • Urinalysis to look for blood or infection  
  • Urine culture to show an infection  
  • Uroflow to determine how fast the urine flows out  
  • Urodynamic testing - 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 tube inserted through the urethra into the bladder) will 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 provider.

Expectations (prognosis)
If diagnosed early, most causes of BOO can be treated with great success. 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 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 have symptoms of bladder outlet obstruction, call your provider. Early diagnosis is important and can often lead to a simple and effective cure.

BOO may be prevented by preventing the underlying cause of obstruction.

Johns Hopkins patient information

Last revised: December 3, 2012
by Martin A. Harms, M.D.

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