Post Void Residuals

Basic Facts

  • The term post-void residual refers to the amount of urine remaining in the bladder after normal urination.
  • An excessive post-void residual volume is evidence of a voiding dysfunction (a problem with urinating or bladder emptying).
  • The volume of residual urine can be measured either directly, with a catheter inserted into the bladder, or indirectly, with an ultrasound scan.

Post-void residual refers to the amount of urine left in the bladder after urination. Post-void residual testing is used to assess the degree of bladder dysfunction. There are two types of this test: in-and-out catheterization and transabdominal or pelvic ultrasound.

There is no need for any special preparation, but the patients should ask the physician or technician about instructions for specific tests.


In-and-out catheterization. Shortly after the patient urinates, the physician, nurse, or medical assistant will insert the catheter through the urethra into the bladder to drain and measure the remaining urine.

Ultrasound. Ultrasound uses high-frequency sound waves to highlight fluid-filled structures in the body. A skilled radiographic technician or ultrasonographer instructs the patient to lie down on a table and applies a conductive gel to the abdomen. The technician glides the transducer over the gel-covered area to emit sound waves through the skin, which bounce back to the transducer as echoes. The transducer converts the returning echoes into electrical signals that calculate the volume of urine remaining in the bladder. The technician will request that the person remain still during the test to ensure that images are clearly captured.


Following post-void residual testing, patients can resume normal activities.


In-and-out catheterization. In rare cases, the complications from this test may include:

  • Discomfort;
  • Injury to the urethra;
  • Urinary tract infection; and
  • Infection caused by bacteria being delivered to the urethra by the catheter.

Ultrasound. This test carries no identified risks and can be performed as often as necessary.

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