The question “when should a bladder scan be performed?” comes up frequently in ward, theatre, community, and nursing care settings because bladder ultrasound scanning is now a standard part of many urinary care pathways.
A bladder scan is a non-invasive bladder ultrasound scan used to estimate bladder volume at the bedside, commonly to support urinary retention bladder scan assessment or to estimate post void residual bladder scan (PVR) after a patient voids. Used well, scanning can reduce unnecessary catheterisation and support safer, faster decision-making. Used poorly—without clear indications, timing, or technique—it can create misleading numbers.
This guide summarises common bladder scan indications, practical bladder scan nursing guidelines, and how to apply the bladder scanning procedure safely in clinical practice. Oras Medical supports clinical education for safe point-of-care bladder scanning and appropriate device selection.
Key Takeaways
A bladder scan should be performed when the result will support a clinical decision—most commonly in urinary retention assessment or PVR workflows.
Bladder scan indications include suspected retention, post-operative monitoring, voiding trials, and evaluation of incomplete bladder emptying symptoms.
Timing and context are critical: for post void residual bladder scan, scan promptly after voiding and document times.
Scan results are estimates and can be affected by technique and confounders (bowel gas, obesity, ascites, pregnancy, pelvic masses).
If results do not fit the clinical picture, repeat the scan, reassess technique/positioning, and escalate or arrange formal imaging when needed.
What is a bladder scan and what does it tell you?
A bladder scan is a bedside ultrasound assessment designed to estimate how much urine is currently in the bladder. Most modern scanners are purpose-built to guide probe placement and provide an automated volume estimate. Clinicians use the result to support decisions such as whether urinary retention is likely, whether the bladder is emptying adequately after voiding, or whether repeat monitoring is needed.
A key point for safe practice is that a bladder scan provides an estimate, not a guaranteed exact measurement. It should be interpreted alongside symptoms, examination, vital signs, fluid balance context, and your local clinical pathway. When a decision is high-stakes—such as catheterisation, escalation for suspected obstruction, or discharge planning—the scan should be one part of the overall assessment.
Read more: How Much Does a Bladder Scanner Cost in the UK? A Buyer’s Guide
General principle: scan when the result changes what you do
The simplest answer to “when should a bladder scan be performed?” is: when the scan result will change your next step. Scanning without a clear clinical question can lead to over-testing, confusing documentation, and unnecessary interventions. Before scanning, identify the question you are trying to answer, such as:• Is the bladder distended in a patient who has not voided?• What is the post-void residual after a voiding trial?• Should we monitor again, escalate, or follow a catheter pathway?• Are symptoms more likely due to retention or another cause?When the answer will influence your action, scanning has a clear purpose.
Bladder scan indications in clinical practice
Below are common indications for bladder scanning. Always align with local policy and scope of practice.
1) Suspected urinary retention (bladder scan in urinary retention)
One of the most common bladder scan clinical indications is suspected urinary retention. Consider scanning when a patient has not voided within an expected timeframe, has suprapubic discomfort, reports difficulty initiating urination, has a weak stream, or has symptoms suggestive of incomplete emptying. A urinary retention bladder scan can help determine whether the bladder is distended and whether a retention pathway should be followed.
In acute settings, retention risk can increase after surgery or anaesthesia, with opioid use, with anticholinergic medications, in neurological conditions, and with significant constipation. Bladder scanning can help distinguish retention from other causes of discomfort or low urine output, supporting safer decisions about observation, encouragement to void, or escalation.
2) Post-operative monitoring
Post-operative urinary retention is a recognised risk, especially after procedures involving regional anaesthesia, prolonged surgery, high opioid requirements, or limited mobility. Many perioperative pathways include bladder scanning at defined intervals or based on symptoms. Scanning can support early identification of retention and may reduce unnecessary catheter use when used within a structured pathway.
3) Post void residual bladder scan (PVR) after voiding
A post void residual bladder scan is performed to estimate how much urine remains after a patient voids. It is commonly used in urology clinics, continence services, and voiding trial pathways. The key to accuracy is timing: scan promptly after the patient voids (within your local policy window) and document both the time of void and the time of scan.
PVR interpretation must be contextual. A single PVR number should not be treated as a universal “normal vs abnormal” threshold for every patient. Symptoms, risk factors, and local protocols determine what action is appropriate.
4) Voiding trials and catheter removal pathways
After catheter removal, bladder scanning is often used to assess whether the bladder is emptying adequately and to guide decisions about repeat monitoring, fluid encouragement, or escalation. Scanning can reduce the need for re-catheterisation in some cases by providing objective information that supports observation and repeat assessment rather than immediate invasive intervention.
5) Lower urinary tract symptoms and incomplete emptying
Patients with lower urinary tract symptoms—such as frequency, urgency, nocturia, hesitancy, or a sensation of incomplete emptying—may benefit from bladder scanning as part of an assessment. In outpatient pathways, scanning can support evaluation of bladder emptying and help guide next steps, including referral or further diagnostic work.
6) Neurogenic bladder and selected specialist pathways
In some neurological conditions, bladder dysfunction may require monitoring under specialist guidance. Bladder scans can support trending volumes and PVR in agreed pathways. Because these cases can be complex, actions should follow local specialist protocols.
Read more: 2D vs 3D Bladder Scanners: What’s the Difference?
When not to rely on a bladder scan alone
Bladder scanning is helpful, but there are scenarios where you should not rely on a scan result in isolation. Examples include severe pain, systemic illness, or red-flag features where urgent medical review is needed; repeated readings inconsistent with symptoms or examination; inability to obtain a reliable scan; or confounders such as known ascites, pregnancy, or suspected pelvic mass. In these situations, repeat scanning may help, but senior review and/or formal imaging may be required depending on the clinical context.
Bladder scanning procedure: practical guidance
Exact steps vary by device, but the following bladder scanning procedure principles apply to most scanners and help improve reliability.
Step 1: Prepare the patient
Explain the scan and obtain consent as appropriate.
Ensure privacy and comfort; expose the lower abdomen while maintaining dignity.
Position the patient consistently (supine if possible) and document if alternative positioning is used.
Step 2: Confirm indication and timing
Document the reason for scanning (e.g., suspected retention, PVR after void, post-op monitoring).
For PVR, record time of void and time of scan.
Review relevant context such as post-op status, medication effects, constipation, and fluid balance notes.
Step 3: Probe placement and targeting
Most bladder scanners require the probe to be placed midline just above the pubic symphysis and angled slightly posteriorly toward the bladder. Use adequate gel and gentle, steady pressure. If your device provides a targeting guide or preview image, use it to centre the bladder before capturing a measurement.
Avoid scanning too low where the pubic bone blocks the beam.
Avoid scanning too high where the bladder may be missed.
Make small adjustments rather than large movements; re-centre and repeat if needed.
Read more: Common Bladder Scanning Mistakes and How to Avoid Them
Step 4: Repeatability and documentation
Repeat the scan if the estimate does not fit the clinical picture or if targeting appears poor.
Document the volume estimate with context: indication, position, timing (especially for PVR), and action taken.
If your pathway requires it, record whether the measurement was repeated and which value was used.
Bladder scan nursing guidelines: safe interpretation and next steps
Local bladder scan nursing guidelines usually connect scan results to actions in a catheter/continence pathway. While thresholds vary, the safe approach is consistent: interpret the estimate alongside symptoms, risk factors, and examination, and follow local escalation criteria. Because thresholds and protocols differ between settings, use locally approved decision support and document the rationale for actions taken.
Common pitfalls: when scans mislead
Pitfall 1: Scanning too long after void (PVR timing error)
If a PVR scan is delayed, refilling can occur and the residual estimate may appear higher. Always document timing and scan promptly according to local policy.
Pitfall 2: Acting on one unexpected reading
A single outlier should be repeated. Reposition the probe, reassess targeting, and repeat before making an invasive decision.
Pitfall 3: Confounders (ascites, bowel gas, pregnancy)
Free fluid or altered anatomy can affect estimates. If confounders are likely and results are inconsistent, escalate for review or formal imaging.
Pitfall 4: Poor documentation
Numbers without indication, timing, and action are difficult to interpret and audit. Standardise documentation fields and encourage consistent handover.
Setting-specific examples
Hospitals
In hospitals, bladder scanning is common after surgery, in acute urinary retention assessment, and during voiding trials. The focus is on timely scanning, repeatability, and clear escalation pathways to reduce harm and avoid unnecessary catheters.
Nursing and residential care
In nursing care, bladder scanning can support non-invasive assessment for frail older adults, reduce unnecessary catheterisation, and provide objective information to guide escalation. Clear protocols and staff competency are essential.
Urology and continence clinics
In outpatient urology, scanning is commonly used for PVR measurement and symptom evaluation. The emphasis is on correct timing, consistent technique, and using results to guide further investigation or management.
Read more: Types of Bladder Scanners: Handheld, Portable, and Wireless
Frequently asked questions
Can you perform a bladder scan as a routine check?
Routine checks without a clinical question are usually not helpful. Scans are most valuable when they support a decision in a defined pathway, such as retention assessment or PVR measurement.
What if the bladder scan result conflicts with symptoms?
Repeat the scan, reassess technique and patient position, consider confounders, and escalate if uncertainty persists—especially if the patient is distressed or clinically unwell.
Do bladder scan thresholds apply to every patient?
No. Thresholds vary by pathway, clinical setting, and patient risk factors. Follow local protocols and clinical judgement rather than relying on a single universal cut-off.
Conclusion
A bladder scan should be performed when the result will guide clinical action—most commonly for urinary retention assessment, post-operative monitoring, and post void residual workflows. Safe practice depends on clear indications, correct timing, consistent technique, repeat scans for unexpected readings, and strong documentation aligned with local nursing guidelines and escalation pathways. When results do not fit the clinical picture, repeat the scan and escalate rather than relying on a single estimate.
References (for clinician use)
Implement local practice using your bladder scanner manufacturer’s instructions for use, your organisation’s continence/catheter pathways, and infection prevention policies. For escalation criteria and decision thresholds, follow locally approved urology/continence guidance and governance requirements.
