Bladder scanners and urinary catheterisation are both used in urinary care, but they serve different clinical purposes. A bladder scanner is a non-invasive tool that estimates bladder volume (and often post-void residual volume, PVR) using ultrasound. Urinary catheterisation is an invasive procedure used to drain urine, measure output in specific pathways, or obtain urine in select circumstances. Because catheterisation carries risks—particularly catheter-associated urinary tract infection (CAUTI) and urethral trauma—many organisations aim to reduce unnecessary catheter use.
This comparison explains the clinical benefits of bladder scanners versus catheterisation, highlights catheterisation complications, and outlines when to use a bladder scanner instead of catheterisation (and when catheterisation is still appropriate). Oras Medical supports clinical education around safe point-of-care bladder assessment and device selection.
Key Takeaways
Bladder scanning is a non-invasive bladder assessment that estimates bladder volume and can support urinary retention diagnosis and PVR workflows.
Catheterisation is invasive but may be required to relieve retention, manage specific perioperative pathways, or measure urine output in selected patients.
Catheterisation risks include CAUTI, urethral trauma, bleeding, discomfort, and complications such as blockage or accidental removal.
Bladder scanning benefits include faster point-of-care assessment, reduced unnecessary catheterisation, and support for CAUTI prevention strategies.
A bladder scanner does not replace clinical judgement: scan results are estimates and must be interpreted with symptoms and local protocols.
If the scan result does not match the clinical picture, repeat the scan, reassess technique, and escalate or arrange formal imaging if needed.
What is a bladder scanner?
A bladder scanner is a point-of-care ultrasound device designed to estimate bladder volume. Most modern scanners are purpose-built to guide the operator toward the bladder and produce an automated volume estimate. Bladder scanners are commonly used in hospitals, nursing care, and urology pathways to support:
Suspected urinary retention diagnosis (as a screening estimate of bladder volume).
Post-void residual volume (PVR) checks and voiding trials.
Post-operative monitoring for retention.
Continence and lower urinary tract symptom pathways where objective volume trends are helpful.
A bladder scan is an estimate rather than a direct measurement. Accuracy depends on technique, timing, patient position, and confounders such as obesity, bowel gas, ascites, pregnancy, and pelvic masses. Results should be interpreted in context of symptoms and local guidance.
What is urinary catheterisation?
Urinary catheterisation involves inserting a catheter into the bladder (usually via the urethra) to drain urine. It can be used for short-term or longer-term drainage, to relieve acute retention, or to measure urine output in selected clinical pathways. Catheterisation may be performed as:
Intermittent catheterisation (in-and-out) for bladder emptying or urine sampling when indicated.
Indwelling urethral catheterisation (Foley catheter) for ongoing drainage.
Suprapubic catheterisation in selected cases under appropriate clinical oversight.
Because catheterisation is invasive, it introduces infection and injury risks, requires aseptic technique, and should be used only when clinically indicated.
Read more: Types of Bladder Scanners: Handheld, Portable, and Wireless
Bladder scanner vs catheterisation: what is being compared?
Bladder scanning and catheterisation are not interchangeable tests. They answer different questions:• Bladder scanning estimates how much urine is in the bladder now (and can help estimate PVR after void).• Catheterisation empties the bladder and can provide a direct drained volume at that moment.In many pathways, scanning is used first to avoid unnecessary catheterisation, while catheterisation is reserved for treatment, high-risk monitoring needs, or circumstances where scanning is unreliable or insufficient for decision-making.
Clinical benefits of bladder scanners
1) Non-invasive bladder assessment
The main bladder scanning benefit is that it provides useful information without entering the urinary tract. This can improve patient comfort and dignity, reduce procedural burden on staff, and support decision-making before any invasive intervention is considered.
2) Supports CAUTI prevention by reducing unnecessary catheter use
Reducing catheter-associated infections is a key patient safety priority. Bladder scanners support CAUTI prevention by helping teams avoid unnecessary catheter placement. For example, when a patient is uncomfortable or has not voided, a bedside scan can help clarify whether the bladder is distended or whether another cause should be investigated. Avoiding catheter placement reduces exposure to catheter-related infection risk.
A bladder scanner does not prevent CAUTI on its own. It supports protocols designed to minimise catheter use and catheter days, alongside insertion and maintenance bundles and daily review.
3) Efficient point-of-care bladder assessment
Bladder scanning can be performed at the bedside, making it a practical point-of-care bladder assessment tool in busy wards and nursing care settings. It can support quicker decisions and reduce delays—particularly when patients cannot easily mobilise for formal imaging.
4) Helpful for PVR and voiding trial workflows
PVR checks are time-sensitive and may require repeated measurements over hours or days. When performed promptly after voiding (per local policy), bladder scanning can support PVR assessment without immediate catheterisation. This is often helpful during voiding trials or when tracking response to treatment.
Read more: How Much Does a Bladder Scanner Cost in the UK? A Buyer’s Guide
Catheterisation risks and complications
Urinary catheterisation can be appropriate and necessary, but it carries recognised risks. Common catheterisation complications include:
Catheter-associated urinary tract infection (CAUTI), particularly with prolonged indwelling use.
Urethral trauma, pain, bleeding, or creation of false passage (higher risk with difficult insertions).
Bladder spasms and discomfort; reduced mobility and increased delirium risk in some older adults.
Catheter blockage, encrustation, leakage, and unplanned catheter changes.
Accidental removal or traction injury, especially in confused or agitated patients.
Skin breakdown or pressure injury from tubing/straps, and reduced dignity.
Because of these risks, catheter stewardship programmes aim to use the least invasive option that meets the clinical goal, remove catheters as soon as they are no longer indicated, and maintain strict aseptic technique.
Bladder scanner accuracy vs catheter drained volume
What bladder scanner accuracy means
Bladder scanner accuracy refers to how closely the estimated volume reflects true bladder volume. Accuracy varies by device, operator technique, patient factors, and timing. Treat the scan as an estimate—especially for borderline decisions.
What catheterisation measures (and its limitations)
Catheterisation can provide a direct drained volume at that moment and can relieve symptoms of retention. However, catheterisation is not ‘risk-free accuracy’: it introduces procedural risks, and drained volume can be influenced by incomplete drainage, kinking, patient position, or spasms. Choose the approach that best matches the clinical goal while minimising harm.
When to use a bladder scanner instead of catheterisation
Bladder scanners are often first-line in pathways where the main question is whether the bladder is distended or what the PVR might be. Examples include:
Suspected urinary retention diagnosis when you need an objective estimate before escalating.
Post-operative monitoring where retention is a known risk and repeated checks may be needed.
Voiding trials and PVR measurement to assess emptying without immediate invasive intervention.
Nursing care settings where non-invasive assessment supports comfort and reduces unnecessary procedures.
If the scan suggests low bladder volume, consider other causes of discomfort or low urine output rather than proceeding directly to catheterisation, and follow local escalation pathways.
Read more: Key Features to Look for When Buying a Bladder Scanner in the UK
When catheterisation may be appropriate (even if you have a scanner)
Catheterisation remains appropriate in certain situations, such as:
Acute urinary retention with significant symptoms where prompt drainage is required.
Need for accurate urine output measurement in selected high-acuity pathways when alternatives are not appropriate.
Perioperative protocols that specifically indicate catheter use (balanced with early removal strategies).
When scanning is unreliable, repeatedly inconsistent with symptoms, or technically not feasible.
Specific urological management plans under specialist guidance.
Catheterisation should be performed for a clear indication, using aseptic technique, documented appropriately, and discontinued as soon as clinically appropriate.
How bladder scanners reduce CAUTI risk in real-world practice
Bladder scanners help reduce CAUTI risk by supporting catheter stewardship workflows such as:
Avoiding catheter insertion when bladder volume is low and symptoms suggest another cause.
Supporting intermittent assessment during monitoring rather than defaulting to an indwelling catheter.
Guiding timely decisions during voiding trials to avoid prolonged catheter days.
Improving decision confidence so catheters are used only when indicated.
Scanners are most effective when combined with infection prevention measures including insertion/maintenance bundles, staff training, and daily review of catheter necessity.
Best-practice approach: a safe decision pathway
Step 1: Clarify the clinical question
Is the goal to estimate bladder volume/PVR, confirm suspected retention, relieve symptoms by draining the bladder, or measure urine output? The answer determines whether scanning, catheterisation, or escalation is appropriate.
Step 2: Use bladder scanning for assessment when appropriate
If the goal is assessment, use a bladder scan for a rapid estimate. Improve reliability by using correct timing (especially for PVR), consistent patient position, correct probe placement, and repeating unexpected readings.
Step 3: Escalate when results do not fit the clinical picture
If symptoms are severe or the estimate is inconsistent, repeat the scan and consider confounders. Escalate to senior review and consider formal imaging where appropriate, especially for high-risk decisions.
Step 4: Use catheterisation for treatment/monitoring when indicated
When catheterisation is indicated, use aseptic technique, follow local insertion and maintenance bundles, document the indication, and plan early removal. Daily review of catheter necessity is a key CAUTI prevention step.
Setting-specific considerations
• Bladder scanner in hospitals: supports perioperative monitoring, retention pathways, and PVR checks; catheter use should follow clear indications with early removal plans.• Bladder scanner in nursing care: supports non-invasive bladder assessment in frail older adults and can reduce unnecessary procedures and transfers.• Urology diagnostic tools: scanners support PVR tracking and symptom evaluation; 2D ultrasound or formal imaging may be used for broader anatomical assessment when needed.
Frequently asked questions
Can a bladder scanner replace catheterisation?
A bladder scanner can often replace catheterisation for assessment (estimating bladder volume or PVR) in many pathways, but it cannot replace catheterisation when bladder drainage is needed to treat retention or when a catheter is required for a specific protocol.
Does bladder scanning eliminate infection risk?
No. Bladder scanning avoids the direct infection risks associated with urinary catheterisation, but overall infection prevention still depends on clinical decisions, equipment cleaning, and catheter stewardship when catheters are used.
What should you do if the scan reading seems wrong?
Repeat the scan, reassess technique, consider confounders, and interpret the estimate alongside symptoms and examination. Escalate if uncertainty persists or the decision is high-risk.
Read more: Portable vs Handheld Bladder Scanners: Which Should You Choose?
Conclusion
Bladder scanners and urinary catheterisation are complementary tools. A bladder scanner enables non-invasive bladder assessment, supports evaluation of urinary retention and post-void residual (PVR) workflows, and may help reduce avoidable catheterisation, thereby supporting CAUTI prevention efforts. Catheterisation remains necessary when drainage or specific monitoring is clinically indicated; however, it carries recognised risks and should be performed only for clear indications, with strict adherence to infection prevention practices. The safest approach is to align the chosen tool with the clinical objective, maintain consistent training and documentation, and escalate when scan findings are inconsistent with the overall clinical picture. For available options, please refer to our bladder scanners listed there.
