Definition of Bladder outlet obstruction (BOO)

Reviewed on 3/29/2021

Bladder outlet obstruction (BOO): a blockage at the base of the bladder at the site where urine flows into the urethra to be expelled from the body. Symptoms of bladder outlet syndrome can include feelings of having a full bladder, abdominal pain, inability to urinate or frequently urinating, a slow flow of urine, problems initiating urination (urinary hesitancy), having to urinate at night, and an intermittent urine stream.

Common causes of bladder outlet obstruction include benign prostatic hyperplasia (BPH), bladder stones, bladder or pelvic tumors, and scar tissue (stricture) of the urethra. Bladder outlet obstruction is most common in older men than in other groups. Treatment depends upon the underlying cause. A urinary catheter may be used to relieve the blockage.


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Longo, D.L., et al. Harrison's Principles of Internal Medicine, 18th ed. United States: McGraw-Hill Professional, 2012.

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