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Cystometric study

Cystometric study measures the amount of fluid 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.

Alternative Names

CMG; Cystometrogram

How the Test is Performed

Prior to the cystometric study, you may be asked to urinate (void) into a special container that is interfaced with a computer. This type of study is called a uroflow, during which the following will be recorded by the computer:

  • The time it takes you to begin urinating
  • The size, force, and continuity of your urinary stream
  • The amount of urine
  • How long it took you to empty your bladder

You will then lie down, and a thin, flexible tube (catheter) is gently placed in your bladder. The catheter measures any urine left in the bladder. A smaller catheter is sometimes placed in your rectum in order to measure abdominal pressure. Measuring electrodes, similar to the sticky pads used for an EKG, are placed near the rectum.

A tube used to monitor bladder pressure (cystometer) is attached to the catheter. Water flows into the bladder at a controlled rate. You will be asked to tell the health care provider when you first feel the need to urinate and when your bladder is completely full.

Often, your doctor may need more information and will order tests to evaluate of your bladder function. This set of  tests is often referred to as urodynamics or complete urodynamics.  The combination includes three tests:

  • Measured voiding without a catheter (uroflow)
  • Cystometry (filling phase)
  • Voiding or emptying phase test

For complete urodynamic testing, a much smaller catheter is placed in the bladder. You will be able to urinate around it. Because this special catheter has a sensor on the tip, the computer can measure the pressure and volumes as your bladder fills and as you empty it. You may be asked to cough or push so that the health care provider can check for urine leakage. This type of complete testing can reveal a lot of information about your bladder functions.

For even more information, x-rays can be taken during the test. In this case, instead of water, a special fluid that shows up on x-ray is used to fill your bladder. This type of urodynamics is called videourodynamics.

How to Prepare for the Test

No special preparations are needed for this test.

For infants and children, preparation depends on the child's age, past experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:

How the Test will Feel

There is some discomfort associated with this test. You may experience:

  • Bladder filling
  • Flushing
  • Nausea
  • Pain
  • Sweating
  • Urgent need to urinate

Why the Test is Performed

The test will help determine the cause of bladder voiding dysfunction.

Normal Results

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

What Abnormal Results Mean

Abnormal results may be due to:

Risks

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

Considerations

This test should not be done if you have a known urinary tract infection. Existing infection increases the possibility of false test results. The test itself increases the possibility of spreading the infection.

References

Nitti V. Urodynamic and videourodynamic evaluation of voiding dysfunction. In: Wein AJ, ed. Campbell-Walsh Urology. 10th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 62.

Lentz GM. Urogynecology: Physiology of micturition, voiding dysfunction, urinary incontinence, urinary tract infections and painful bladder syndrome. In: Lentz GM, Lobo RA, Gershenson DM, Katz VL, eds. Comprehensive Gynecology. 6th ed. Philadelphia, PA: Mosby Elsevier; 2012:chap 21.

Updated: 8/25/2014

Scott Miller, MD, Urologist in private practice in Atlanta, GA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.


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