What Is a Post-Void Residual Urine Test?

When you pee, not all the urine gets emptied from your bladder. If you have urinary problems, your doctor may need to know how much is left there. A post-void residual urine test can tell them.

If the test shows there’s too much there after you pee, that can be a sign of a few things:

  • There's an infection in your kidneys, bladder, or the tubes that connect them.
  • Your bladder is blocked at the end so urine can’t flow out.
  • Your bladder has trouble pushing urine out.
  • Your prostate is enlarged.

There are two ways to do a post-void residual urine test:

  • Catheter: A nurse slides a thin, flexible tube called a catheter through your urethra (where pee comes out) and into your bladder, then takes out the urine.
  • Ultrasound: A machine uses sound waves to show live images of your bladder so your doctor can see how much urine is there.

Some researchers think catheters measure urine in the bladder better than an ultrasound, while others think the two tests work equally well.

Catheter

A nurse will ask you to pee right before the test. Then they’ll give you medicine to numb the area. They’ll slide the catheter through your urethra, take out the urine in your bladder, and measure how much was taken out.

There are a few things to think about with the catheter method:

  • It may feel uncomfortable.
  • It might make you more likely to get an infection.
  • It’s rare, but it could injure your urethra.

Ultrasound

With this method, after you pee, the nurse will hold the ultrasound wand against your belly. Pictures of your bladder will show up on a monitor, and your doctor will use them to measure the urine there.

This method has a few advantages over the catheter method.

  • Because nothing goes inside your body, there’s no chance of injury or infection.
  • The sound waves are painless.
  • The nurse doesn’t need to see your private parts.
  • It’s safer for children and doesn’t stress them out as much.

But an ultrasound might not work for some people. For example, if you’re obese, the machine may not be able to get clear pictures of your bladder.

WebMD Medical Reference Reviewed by Minesh Khatri, MD on February 12, 2018

Sources

SOURCES:

Reviews in Urology: “Evaluation of Voiding Dysfunction and Measurement of Bladder Volume.”

National Institute of Diabetes and Digestive and Kidney Diseases: “Urodynamic Testing,” “Urinary Tract Imaging.”

Ontario Health Technology Assessment Series: “Portable Bladder Ultrasound: An Evidence-Based Analysis.”

Canadian Family Physician: “Ultrasound bladder scanner presents falsely elevated postvoid residual volumes.”

Cleveland Clinic: “Bladder Outlet Obstruction.”

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