Bladder Ultrasound: Investigating Urinary Frequency

Ultrasound 06 October, 2026

Understanding bladder ultrasound

What is ultrasound?

An ultrasound scan passes painless, high-frequency sound waves into your body to create real-time images of your tissues.

The sound waves bounce off boundaries between areas of different densities. The reflected sound waves are detected and converted into live, digital, greyscale images of your tissues.

What does bladder ultrasound check for?

A bladder ultrasound scan is also called bladder ultrasonography. It can reveal your:

bladder volume
bladder shape#
bladder wall thickness
ability to empty your bladder (also called voiding)

Although bladder ultrasound is often used to investigate the underlying causes of bladder symptoms, it’s sometimes used to check whether patients need to have a Foley catheter fitted (a tube that drains urine from your bladder into a bag). This is called urethral catheterisation or bladder catheterisation.

Common symptoms leading to bladder ultrasound

Your doctor may recommend that you have a bladder ultrasound scan if you have any of the following symptoms:

a stop-start or weak stream when you pass urine
difficulty starting to urinate
a feeling that your bladder is not empty after urinating
sudden urges to urinate
urine leakage eg due to overflow incontinence (when the bladder doesn’t empty fully and then leaks)
urinating more often than normal, including at night

What conditions can a bladder ultrasound scan detect?

A bladder scan can help detect the causes of inadequate emptying of the bladder, which is called urinary retention. Retained urine and structural abnormalities can be seen on an ultrasound scan.

There are 2 main types of urinary retention.

Acute urinary retention – a sudden inability to empty your bladder, with little to no urine output. This is a medical emergency and can cause intense suprapubic pain.
Chronic urinary retention – an inability to empty your bladder that develops gradually over time.

Both types of urinary retention should always be investigated as they have a risk of serious complications, such as acute kidney injury.

In addition to chronic (long term) and acute retention, if you have surgery, you may experience postoperative urinary retention. This is due to the effects of general anaesthesia.

Causes of urinary retention

Chronic retention can be caused by certain medications or by bladder outflow obstruction. Bladder outflow obstruction is a type of obstructive uropathy, where there’s a problem at the base of the bladder that stops urine from flowing out of the urethra.

The urethra is the tube that urine passes through to leave your body. In older males, an enlarged prostate, also known as benign prostatic hyperplasia, is the most common cause of bladder outflow obstruction.

An enlarged prostate pushes against the bladder and urethra, making it difficult to empty the bladder, but also causing frequent urination. This can also occur in prostate cancer.

Other causes of bladder outflow obstruction, which is also known as urinary outlet obstruction, include:

bladder or kidney stones – these can become lodged in the urethra and block it
damage to the nerves supplying the ring of muscle that opens the bladder into the urethra – this can be caused by brain or spinal tumours, neurologic disease, pelvic surgery, stroke or spinal cord injury
large ovarian cysts in women – these can press against the bladder or urethra
pelvic organ prolapse in women – the bladder or womb sinks lower into the pelvis and causes a kink in the urethra
urinary tract infections – this leads to inflammation and swelling that can narrow or block the urethra

Post void residual urine test to diagnose urinary retention

The main test for the diagnosis of urinary retention is a post void residual urine test. This can be performed either by bladder catheterisation, or during a bladder scan, or transvaginal ultrasound scan.

When you urinate, your bladder empties. To check your residual urine volume, your care team will use dedicated bladder scanners to image your bladder once you’ve passed as much urine as possible.

An ultrasound probe will be passed over your lower abdomen and pelvic area. The images collected are used to measure PVR (post void residual) volume i.e. the amount of urine left in your bladder.

Different PVR volumes are considered high depending on your age and health. If you have an elevated PVR, your doctor will consider this as part of their clinical decision making. They will then explain your treatment options.