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- The amount of urine lost (the patient may be asked to catch and measure urine in a measuring cup during a 24-hour period)
- Whether the urge to urinate was present
- Whether the patient was involved in physical activity at the time
The office visit should consist of a thorough physical examination, checking for abnormalities or enlargements in the rectal, genital, and abdominal areas that may cause or contribute to the problem.
Measuring Postvoid Residual Urine Volume
The postvoid residual urine volume (PVR) measures the amount of urine left in the bladder after urination:
- Normally, about 50 mL or less of urine is left
- More than 100 mL suggests an abnormality and requires further tests
- More than 200 mL is a definite sign of abnormalities
Use of a Catheter. The most common method for measuring PVR uses a catheter, which is inserted into the urethra after a few minutes of urination. The advantage of the catheter is that it can also collect urine for analysis, but it can be uncomfortable and lead to urinary tract infections.
Ultrasound. Ultrasound may also be used to measure the volume of remaining urine.
Cystometry measures the bladder's ability to retain urine at different capacities and pressures. It uses a catheter and can be performed at the same time as the PVR test.
Subtraction Cystometry. Although procedures vary, the basic steps for the technique are as follows:
- The patient empties the bladder as much as possible.
- A double-channel catheter is inserted through the urethra and into the bladder. It is used to fill the bladder with water and to measure pressure. Another catheter is inserted into the rectum or vagina, which is used to measure abdominal pressure.
- While water is instilled through the tube into the bladder, the pressure in the bladder and abdomen are measured and the results are recorded in a computing device.
- During the process, the patient informs the doctor about any changes in the need to urinate, including the initial need to urinate, a normal desire to urinate, and a strong need to urinate.
- Often during this process, the patient is asked to cough, bounce up and down, or even walk in place. The patient may also be asked to strain as if he or she is having a bowel movement. This is called the Valsalva maneuver. The point at which leakage occurs during this action is called the Valsalva leak point pressure, which might be a useful measurement for determining treatment.
- When the urge to urinate is strong, the doctor stops this portion of the test.
- A calculation is then made using bladder and abdominal pressure measurements as well as volume and flow rate of the urine. The result provides the doctor with an assessment of detrusor contractions.
Review Date: 07/26/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.