A bladder ultrasound test is used in the urologist's office to measure the amount of urine in the bladder, to look for stones, to measure the bladder wall thickness, and to look for elevation of the bladder by an enlarged prostate. The most common use of bladder ultrasound is to measure how much urine is left behind in the bladder after you are done urinating, an amount called the post-void residual.
The patient lies on his or her back, and the pants are pulled down so that the lower abdomen is exposed. Ultrasound gel is placed on the lower abdomen and the ultrasound probe is placed gently on the skin. It usually takes less than two minutes to complete a bladder ultrasound test.
You should come to the office with a full bladder, or come early and drink fluids at the office until the bladder is full. If the purpose of the test is to measure the post-void residual urine volume, then you will be asked to empty your bladder first, and then the bladder will be scanned immediately afterwards. If the purpose of the test is to take pictures of the full bladder then you will be taken to the ultrasound room first, the bladder ultrasound test will be performed, and then you will be asked to empty your bladder.
Bladder ultrasound is extremely safe, it uses sound waves that you cannot hear to take pictures of internal structures. This is the same technology used to take pictures of pregnant women and their babies, so it is very safe.