(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 or 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

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

  • Two kidneys. A pair of purplish-brown organs located below the ribs toward the middle of the back. Their function is to remove liquid waste from the blood in the form of urine, keep a stable balance of salts and other substances in the blood, and produce erythropoietin, a hormone that aids the formation of red blood cells.
    The kidneys remove urea from the blood through tiny filtering units called nephrons. Each nephron consists of a ball formed of small blood capillaries, called a glomerulus, and a small tube called a renal tubule. Urea, together with water and other waste substances, forms the urine as it passes through the nephrons and down the renal tubules of the kidney.

  • Two ureters. Narrow tubes that carry urine from the kidneys to the bladder. Muscles in the ureter walls continually tighten and relax forcing urine downward, away from the kidneys. If urine backs up, or is allowed to stand still, a kidney infection can develop. About every 10 to 15 seconds, small amounts of urine are emptied into the bladder from the ureters.

  • Bladder. A triangle-shaped, hollow organ located in the lower abdomen. It is held in place by ligaments that are attached to other organs and the pelvic bones. The bladder's walls relax and expand to store urine, and contract and flatten to empty urine through the urethra. The typical healthy adult bladder can store up to two cups of urine for two to five hours.

  • Two sphincter muscles. Circular muscles that help keep urine from leaking by closing tightly like a rubber band around the opening of the bladder.

  • Nerves in the bladder. These nerves alert a person when it is time to urinate or empty the bladder.

  • Urethra. The tube that allows urine to pass outside the body.

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:

  • Urinary incontinence. Loss of bladder control. 

  • Urinary retention. Inability to empty the bladder completely.

  • Neurogenic bladder dysfunction. Improper function of the bladder due to an alteration in the nervous system such as a spinal cord lesion or injury.

  • Spinal cord injury

  • Multiple sclerosis. An unpredictable disease of the central nervous system that can be relatively benign, disabling, or devastating, leaving the patient unable to speak, walk, or write.

  • Diabetes. A disorder that occurs when the body is not able to use sugar for growth and energy for daily activities.

  • Tabes dorsalis. A progressive disorder of the nervous system that involves the spinal cord and causes interference with normal reflexes such as voluntary urinary control. 

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:

  • Urinary tract infection

  • Autonomic reflex (severe headache, increased blood pressure, lower heart rate, sweating and flushing) in patients who have a spinal cord injury or spinal cord lesion

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:

  • Your doctor will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.

  • You may be asked to sign a consent form that gives your permission to do the procedure. Read the form carefully and ask questions if something is not clear.

  • Generally, no prior preparation, such as fasting, fluid restriction, or sedation is required.

  • If you are pregnant or suspect that you may be pregnant, you should notify your health care provider.

  • Notify your doctor if you are sensitive to or are allergic to any medications, latex, tape, and anesthetic agents (local and general).

  • Notify your doctor of all medications (prescribed and over-the-counter) and herbal supplements that you are taking.

  • Notify your doctor if you have a history of bleeding disorders or if you are taking any anticoagulant (blood-thinning) medications, aspirin, or other medications that affect blood clotting. It may be necessary for you to stop these medications prior to the procedure.

  • Notify your doctor if you suspect that you have a urinary tract infection.

  • You may be given an antibiotic a day or so before the procedure.

  • Patients who have problems with constipation may be given an enema prior to the procedure.

  • Based on your medical condition, your doctor may request other specific preparation.

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:

  • Fever and/or chills

  • Abdominal pain

  • Continued or increased blood in the urine

  • Urine output is less than usual amount

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 health care provider 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