Cystometric study

Alternative names 
CMG; Cystometrogram


Cystometric study uses a device to pump water into the bladder. The device then measures the amount of fluid present in the bladder when you first feel the need to urinate, when you are able to sense fullness, and when your bladder is completely full.

How the test is performed

You are asked to void (urinate). The time required to begin voiding and the size, force, and continuity of the urinary stream is recorded. The amount of urine, how long the voiding took, and the presence of straining, hesitancy, and dribbling are also recorded.

You are then asked to lie down. A catheter (a thin, flexible tube) is gently positioned in the bladder, and any urine left in the bladder is measured and recorded. A catheter is then placed in the rectum and measuring electrodes are placed in the perineum (area near the rectum).

Next, the thermal sensation is evaluated. Room-temperature saline solution is instilled into the bladder, followed by warm water.

You need to tell the health care provider what, if any, sensations are felt. The water is then drained from the bladder.

A cystometer (a tube used to monitor bladder pressure) is connected to the catheter. Water or carbon dioxide gas is slowly introduced into the bladder at a controlled rate.

You will need to tell the provider when you first feel the need to urinate. The pressures and volumes are recorded. When the bladder is full, you must urinate, and the pressure of the urination is recorded.

The bladder is again drained of any residual urine and the catheter is removed.

How to prepare for the test

No special preparations are necessary for this test.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child’s age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child’s age:

  • Preschooler test or procedure preparation (3 to 6 years)  
  • Schoolage test or procedure preparation (6 to 12 years)  
  • Adolescent test or procedure preparation (12 to 18 years)

How the test will feel
There is some discomfort associated with this test. You may experience pain, flushing, sweating, nausea, bladder filling, and a sense of an urgent need to urinate.

Why the test is performed
The test is performed to help determine the cause of bladder/voiding dysfunction.

Normal Values
Normal values vary and should be discussed with your health care provider.

What abnormal results mean

The test might indicate a cause for urinary tract infection, diminished bladder capacity, multiple sclerosis, stroke, a spinal cord injury, bladder outlet obstruction, or overactive bladder.

What the risks are
There is a slight risk of urinary tract infection and blood in the urine.

Special considerations
This test should not be done if you have a known urinary tract infection. An existing infection increases the possibility of false test results, and the test increases the possibility of spreading of the infection.

Johns Hopkins patient information

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

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