Robert Wood Johnson University Hospital



(Cystometrogram, CMG)

Procedure Overview

What is cystometry?

Cystometry is a diagnostic procedure used to identify problems with the filling and emptying of the urinary bladder. This test measures the amount of volume/urine in the bladder compared with the bladder pressure and the person's perception of bladder fullness. Cystometry provides information about the muscle function, mechanics, and nerve response of the bladder and urinary tract.

A normally functioning bladder sends messages to the brain via nerve pathways when it needs emptying. The spinal cord then transmits a message to the bladder to contract and begin the reflex of urinating. A person can override this reflex voluntarily by holding his or her urine.

Some medical conditions may interfere with the muscular function or nerve pathways between the bladder and the brain. These conditions may lead to urinary incontinence (loss of bladder control) or urinary obstruction. Cystometry may be indicated to determine the source of such problems. It is often done together with Uroflowmetry, which provides a measurement of urine speed and volume, and an estimation of post-void residual (how much urine remains in the bladder).

Other related procedures that may be used to evaluate bladder or urinary problems include cystography and intravenous pyelogram (IVP). Please see these procedures for additional information.

How does the urinary system work?

Illustration of the anatomy of the urinary system, front view
Click Image to Enlarge

The body takes nutrients from food and converts them to energy. After the body has taken the food that it needs, waste products are left behind in the bowel and in the blood.

The urinary system keeps chemicals, such as potassium and sodium, and water in balance, and removes a type of waste, called urea, from the blood. Urea is produced when foods containing protein, such as meat, poultry, and certain vegetables, are broken down in the body. Urea is carried in the bloodstream to the kidneys.

Other important functions of the kidneys include blood pressure regulation, and the production of erythropoietin, which controls red blood cell production in the bone marrow.

Urinary system parts and their functions:

Reasons for the Procedure

Cystometry may be recommended to evaluate problems related to the muscle function of the bladder and urethra. Conditions that may cause functional problems of the bladder and urethra may include, but are not limited to, the following:

Problems in the urinary system can also be caused by aging, other illness, or injury. Weak bladder muscles may result in not being able to empty your bladder completely. Weak muscles of the sphincters and pelvis can lead to urinary incontinence because the sphincter muscles cannot remain tight enough to hold urine in the bladder, or the bladder does not have enough support from the pelvic muscles to stay in its proper position.

Urodynamics is a test that looks at how the bladder and urethra are storing and releasing urine. A doctor may use the results from other procedures, such as cystography and IVP, along with the results of a cystometry procedure to formulate a diagnosis.

There may be other reasons for your doctor to recommend cystometry.

Risks of the Procedure

Some complications of cystometry may include, but are not limited to, the following:

Cystometry is contraindicated for patients with a urinary tract infection.

There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.

Straining with urination and certain medications may interfere with a cystometry procedure.

Before the Procedure

During the Procedure

Cystometry may be performed on an outpatient basis or as part of your stay in the hospital. Procedures may vary depending on your condition and your and your doctor's practices.

Generally, cystometry follows this process:

  1. You will be asked to remove your clothing, jewelry, or other objects that may interfere with the procedure
  2. If you are asked to remove clothing, you will be given a gown to wear.
  3. You will be asked to empty your bladder. During urination, the amount, flow rate, and voiding pressure will be recorded. Do not strain to urinate as this may alter the test results.
  4. You will be positioned on your back on the examination table.
  5. A catheter will be inserted into the urethra until it reaches the bladder. You may experience some discomfort during the catheter insertion.
  6. An additional catheter or pressure probe may be inserted into the rectum or vagina to measure pressure in the abdomen. Alternately, adhesive electrodes may be placed on either side of the anal opening to measure muscle function.
  7. A small amount of room temperature fluid will be injected through the catheter into the bladder. Next, an equal amount of warmed fluid will be injected. You will be asked to describe all sensations, such as warmth, the need to urinate, discomfort or pain, and nausea.
  8. The fluid will be drained from the catheter.
  9. The catheter will be connected to a measuring device called a cystometer (a tube to measure bladder pressure).
  10. Fluid or gas will be slowly injected through the catheter into the bladder. You will be asked to tell when you first feel the urge to urinate and when you feel that you must urinate. Bladder pressure will be recorded during this time.
  11. When the bladder is completely full, you will be asked to empty your bladder while pressure is being recorded.
  12. In some situations, medication that can affect the bladder’s muscle tone may be given, and the procedure will be repeated in 20 to 30 minutes.
  13. When all tests have been performed, the catheter will be removed. The rectal probe or adhesive patches will also be removed, if used.
  14. You may experience discomfort during this procedure, such as flushing, sweating, nausea, pain, bladder filling, urgent need to urinate.

After the Procedure

There is no special type of care required after cystometry. You may resume your usual diet and activities unless your doctor advises you differently.

You will be encouraged to drink extra fluids to dilute the urine and reduce urinary discomfort such as burning.

You may feel some urinary discomfort, but it should lessen over time. You may be offered a warm sitz bath or a tub bath as a comfort measure.

You may notice blood in your urine for a period of time after the procedure. The amount of blood will reduce gradually over time.

Your doctor may prescribe an antibiotic to prevent a urinary tract infection.

Notify your doctor to report any of the following:

Your doctor may give you additional or alternate instructions after the procedure depending on your particular situation.

Online Resources

The content provided here is for informational purposes only, and was not designed to diagnose or treat a health problem or disease, or replace the professional medical advice you receive from your doctor. Please consult your doctor with any questions or concerns you may have regarding your condition.

This page contains links to other websites with information about this procedure and related health conditions. We hope you find these sites helpful, but please remember we do not control or endorse the information presented on these websites, nor do these sites endorse the information contained here.

American Urological Association

National Institute of Diabetes and Digestive and Kidney Diseases

National Institutes of Health (NIH)

National Kidney and Urologic Diseases Information Clearing House

National Kidney Foundation

National Library of Medicine


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