Skip to main content

Key Points

  • We monitor your bladder pressure because constant high pressure can damage the kidneys. 
  • A cystometrogram can’t be done if you have symptoms of a urinary tract infection. 

What is a cystometrogram (CMG)?

We use a cystometrogram (CMG) to check how well your bladder functions during filling. A CMG also measures the pressure inside your bladder and the strength of your bladder muscle. The results of a CMG help us identify the size of your bladder and the amount of urine it can hold without leaking or causing problems for your kidneys. It is generally well-tolerated and not painful to our patients.

Why do we do CMGs?

People who have spina bifida, spinal cord injuries and cerebral palsy frequently have neurogenic bladders. This means that the bladder doesn’t function in a typical way because the nerves that connect to the bladder have been affected. It is important to monitor and manage the pressure in your child’s bladder to prevent continued high pressure from damaging the kidneys. 

Where will this be done?

You’ll have your procedure in a private room at our St. Paul Campus. Music, movies and aromatherapy are available to create a comfortable environment. 

What do I need to do to get ready for the procedure?

Please review the information provided regarding signs and symptoms of a urinary tract infection (UTI). A CMG cannot be completed if you have a UTI. 

Please review the information provided regarding having a bowel movement prior to your CMG. Constipation or having a full rectum will affect the results of your test and a CMG may not be completed if you are constipated or have a full rectum. 

Day Before Procedure

You must have a bowel movement the day before your procedure. You can accomplish this by using a bowel program that is already established, or by using an over-the-counter rectal suppository or enema. 

What should I bring to my appointment?

  • List of current medicines, dose and frequency 
  • List of allergies 
  • Bladder diary 
  • Your catheterization supplies, if you empty your bladder by catheterization 
  • If you wear a brief or pad, bring a fresh brief or pad for after the procedure
  • A CD or music player, if you prefer to listen to specific music 
  • If you need assistance with communication or relaying information, please have a caregiver accompany you to be sure we communicate accurate information

What will happen during my CMG appointment?

Set Up 

You will lie down in a bed during the procedure. You will remove your undergarments from your waist down and we will cover you with a blanket. 

Two small tubes called catheters will be used to monitor pressures.  Each catheter has a pressure sensor that connects to the CMG machine. We will place one catheter into your bladder to measure the pressure in your bladder. At this time, a urine sample may be taken. The second catheter will be placed in your rectum to measure the pressure in your abdomen outside of your bladder. We use these two pressure readings to figure out the bladder muscle pressure.  

We will place three small sticky electrode patches on your body to help measure the sphincter muscle activity. Two of the electrodes will be placed around your anus and the third near your hip.  


After the catheters have been inserted and the patches placed, the catheter will begin to fill your bladder with sterile saline solution. If you are able to feel your bladder during the filling, we will ask you to let us know what you are feeling. We will record your bladder volume and pressure on a graph. At the end of the procedure, we will let you know when it is time to empty your bladder if you are able to do so. Otherwise, the catheter will be used to empty your bladder. You may use your home catheter to empty your bladder at the end of the test if you prefer.

After the Procedure 

After the CMG is complete, we will remove the catheters and the electrodes. Your skin will be washed and dried, and you may get dressed again. If you are scheduled to have a second test called a Voiding Cystourethrogram (VCUG), the catheter in your bladder may be left in place or may be replaced with a different catheter.  

The results of your testing will be discussed by the urology provider during your next clinic visit. Information from this test will help determine if you would benefit from intermittent catheterization, medicine, or other interventions.

You may immediately return to your regular activities. Please increase your water intake for the rest of the day. Please note that you may have some slight discomfort with urination or catheterization immediately following the test. 

What are the risks of a CMG?

You might have an increased risk of a urinary tract infection (UTI). Please call your primary care clinic if you develop signs and symptoms of a UTI. 

For people with a high spinal cord injury, autonomic dysreflexia could occur. These symptoms include: high blood pressure, severe headaches and sweating. If you become dysreflexic during the procedure, we would stop the CMG. 

If you have a history of autonomic dysreflexia, please alert the provider performing your test to ensure proper precautions are taken. 

When should I call a health care provider?

Please call Telehealth at (651) 229-3890 should you experience: 

  • Signs or symptoms of a urinary tract infection 
  • Urinary retention (inability to void in 12 hours) 
  • Abdominal, back or side pain 
  • Painful urination after 48 hours 
  • Pain not relieved by over the counter pain medications

This information is for educational purposes only. It is not intended to replace the advice of your health care providers. If you have any questions, talk with your doctor or others on your health care team. If you are a Gillette patient with urgent questions or concerns, please contact Telehealth Nursing at 651-229-3890.