What is urodynamics?

Urodynamics, also called a cystometrogram or CMG is a test used to evaluate your bladder’s ability to store and release urine. This test is used to determine the cause of your bladder complaints. Since each type of urinary problem requires specific treatment, this test will allow us to tailor your treatment to your particular needs.

How to prepare?

Please arrive for your procedure on time. Do not empty your bladder for 1 hour prior to your appointment time. You may eat and drink as usual and remain active right up until the time of your cystometrogram.

What to expect?

Once you are settled in the room you will be asked to disrobe from the waist down. A physician or nurse will discuss any urinary problems you are currently experiencing or have experienced in the past. He or she will also take a brief medical history and record which medications you are currently taking.

You will then be asked to empty you bladder into a special commode. This commode can record the rate at which you empty your bladder, as well as the amount of urine you emptied at that particular time. A catheter (a thin, long, flexible tube) is then inserted into the bladder and any urine remaining in the bladder is drained and measured (post-void residual). This catheter will be used to fill your bladder with a sterile saline solution. Then, a second catheter is placed into the rectum. Meanwhile, the physician or nurse will ask you several questions about the sensations you are experiencing. While your bladder is being filled, you will be asked to perform certain activities, such as coughing, or pushing (“bearing down”).

Once you feel that your bladder is filled to capacity, you will be asked to empty it with the catheters in place. A computerized instrument will record the pressures generated by your bladder. The catheters will be removed after the computerized device collects sufficient pressure readings.

The test takes approximately 30 minutes to complete. You may resume your normal activities immediately.

How are the results interpreted?


The amount of urine left in the bladder after urinating, when the urge to urinate is felt, and when urine can no longer be held back are within normal ranges.


One or more of the following may be found:

  • More than a normal amount of fluid remains in the bladder after urinating. A large volume of urine remaining in the bladder suggests the flow of urine out of the bladder is partially blocked or the bladder muscle is not contracting properly to force all the urine out (overflow incontinence).
  • The bladder contains less fluid, or more fluid than is considered normal when the first urge to urinate is felt.
  • The bladder is unable to retain urine when it contains less than the normal amount of fluid for most people.
  • Leaking of urine at any time during the testing.
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