What is considered urinary retention on a bladder ultrasound scan?

From the Guidelines

Urinary retention on a bladder scan is considered when the post-void residual bladder volume is greater than 500 cm3 in asymptomatic patients or greater than 300 cm3 in symptomatic patients. This definition is based on the most recent guidelines from the International Society for Infectious Diseases, updated in 2024 1. The guidelines emphasize the importance of appropriate indications for catheter placement, including the management of acute urinary retention.

Key Points to Consider

• Symptoms of urinary retention may include bladder pain or fullness, persistent urge to void, new incontinence or leaking, or being only able to have frequent small voids.
• A bladder scanner is used to detect the post-void residual bladder volume, providing a non-invasive measurement of bladder volume using ultrasound technology.
• The threshold for considering urinary retention may vary depending on the clinical context, but the guidelines provide a clear indication for asymptomatic and symptomatic patients.

Clinical Implications

• Clinicians should use bladder scans to assess the severity of retention and determine appropriate management, which may include catheterization if the retention is severe or causing symptoms.
• It is crucial to remove catheters placed solely due to the duration of surgery or for decompression for a specific surgical approach after the surgical case, as indicated in the guidelines 1.
• The guidelines highlight the importance of removing catheters as soon as possible to prevent catheter-associated urinary tract infections.

From the Research

Urinary Retention on Bladder Scan

• Urinary retention is often assessed by measuring post-void residual (PVR) urine volume, which can be done using a bladder scanner or urethral catheterization 2, 3.
• There is no universally accepted definition of a significant residual urine volume, but large PVR (>200-300 ml) may indicate marked bladder dysfunction 2.
• A PVR threshold of 100 ml, 150 ml, and 200 ml have been studied, with 150 ml being considered a cost-effective strategy for avoiding postoperative urinary retention and undue health costs 4.
• The accuracy of portable bladder scanners in measuring PVR has been evaluated in various studies, with results showing strong correlations between scan volumes and catheter volumes 3, 5, 6.
• Factors such as age, body mass index, parity, co-existing illness, type of surgical incision, or duration of indwelling catheter do not affect the difference in measurements between bladder scanners and urethral catheterization 3.
• Pelvic organ prolapse does not appear to affect the accuracy of post-void residual urine volume measurement using a portable bladder scanner 6.

PVR Measurement Thresholds

• A PVR threshold of 150 ml is considered a cost-effective strategy, minimizing emergency department visits for postoperative urinary retention and unnecessary clinic appointments 4.
• A PVR threshold of 200 ml may be a cost-effective strategy, but it can lead to increased emergency department utilization and under-detection of postoperative urinary retention 4.
• A PVR threshold of 100 ml may create a healthcare system burden due to increased office voiding trials 4.

Bladder Scanner Accuracy

• Portable bladder scanners have been shown to have high specificity and negative predictive value in predicting catheter volumes of <100 ml 3.
• The use of real-time pre-scan imaging (RPI) can improve the accuracy of bladder scanners in measuring PVR volumes 5.
• Bladder scanners can be a reliable alternative to urethral catheterization for measuring PVR in postoperative patients 3, 5, 6.