Cystometric study

  • Definition
    • 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
  • 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
  • Risks
  • 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.