Flow rate and residual ultrasound | JP Meyer Urology

Flow rate and residual ultrasound

Patient Information

As part of the investigation of problems associated with bladder function, it is often necessary to measure the rate at which urine is passed (the flow rate), and the amount of urine left in the bladder (the residual).

Preparation for the flow rate investigation:

In order to obtain a reliable flow test you need to pass more than 150mls of urine. Begin drinking water early on the day of your investigation. You need to have a full bladder for the test.
To achieve this it is suggested that you:

  1. Drink plenty of water on waking
  2. Pass urine two hours before the test
  3. Continue to drink approximately 4-5 drinks before your appointment

If you do not have a full bladder at the time you come for the test, you can drink water in the waiting room to fill your bladder.


When you have a full bladder, you will be required to pass urine into a machine which measures the rate and volume of your flow and produces a printout.

If the flow test is inadequate, a second flow test may be necessary.
You will then be asked to lie down on a bed for a quick ultrasound scan of your bladder to determine the amount of urine left behind in your bladder after you have passed urine.

This is a painless scan.

Following your flow rate investigation:

In the couple of hours following the test you can expect to pass a lot of urine. I will discuss the results with you at the next appointment or later the same day.