Bladder scanners estimate bladder volume to support decisions about urinary retention, catheterisation and post‑void residual (PVR) measurement. They are widely used because they are fast, non‑invasive and can improve patient comfort when used appropriately. However, results are operator‑ and context‑dependent: small workflow or technique errors can produce misleading readings and, in turn, inappropriate actions.
This guide explains the most common bladder scanning mistakes and provides practical bladder scanner accuracy tips to improve reliability in everyday clinical care (as highlighted across clinical education resources such as those published by Oras Medical).
Key Takeaways
Treat a bladder scan as an estimate and interpret it alongside symptoms, history and local protocol.
Get the basics right: correct timing (especially for PVR), consistent patient positioning and the right device preset/mode.
Probe placement matters: midline just above the pubic symphysis with gentle, steady pressure and small angle adjustments.
Repeat unexpected readings and consider confounders (obesity, bowel gas, pelvic masses, inability to lie flat).
Document context (indication, timing, position, preset, repeats and action taken) to support safe handover and trend monitoring.
Follow manufacturer-approved cleaning and infection prevention steps between patients and maintain staff competency with refreshers.
Why accuracy matters
A bladder scan is an estimate, not a direct measurement. Inaccurate readings can expose patients to unnecessary catheterisation, delay recognition of clinically significant retention, or create confusing trends during monitoring (for example, during a voiding trial). Because catheter decisions carry risks (including discomfort, urethral trauma and infection), interpret the scan alongside symptoms, physical assessment and the broader clinical picture.
Common mistakes before scanning
Mistake 1: Scanning without a clear clinical question
Scanning should be linked to an indication (for example suspected retention, PVR after void, or post‑operative monitoring). Numbers without context are easy to misinterpret, especially during busy shifts or handovers.
How to avoid it:
Document the indication and the planned response according to local protocol.
If symptoms are severe (pain, distress, inability to void) or the picture is unclear, prioritise clinical assessment and escalate rather than relying on one reading.
Mistake 2: Wrong timing for PVR measurement
For PVR, delays after voiding allow the bladder to refill and can inflate the estimate. Timing errors are a frequent reason for unexpectedly high ‘residuals’ in otherwise stable patients.
How to avoid it:
Scan promptly after voiding (commonly within 10 minutes, per local policy).
Record time of void and time of scan so the result can be interpreted correctly.
If there is a delay, interpret the number cautiously and consider repeating after a supervised void.
Mistake 3: Poor positioning or inadequate preparation
Position changes can shift the bladder and affect repeatability, particularly when trending volumes. Poor privacy or explanation can also increase movement and discomfort, which may reduce scan quality.
How to avoid it:
Explain the procedure in simple terms, obtain consent, and ensure privacy.
Use a consistent position (supine where possible) and document alternatives (semi‑recumbent or seated).
Expose the lower abdomen enough to place the probe correctly while maintaining dignity.
Device setup mistakes
Mistake 4: Using the wrong preset or patient setting
Many scanners use presets that influence the volume algorithm. Wrong settings can reduce accuracy and make results less comparable between clinicians.
How to avoid it:
Confirm the correct preset/mode according to the device instructions for use (IFU).
Be aware that anatomy and prior pelvic surgery can affect readings; follow manufacturer guidance for special cases.
Standardise presets in your local SOP and include them in competency checklists.
Mistake 5: Skipping basic equipment checks
Low battery, residue on the probe face, or inconsistent cleaning can degrade performance and infection‑control safety. In settings where scanners are shared across wards or rooms, these basics are essential.
How to avoid it:
Check battery level and probe condition before use; use enough gel for good contact.
Clean and disinfect the probe and device between patients using manufacturer‑approved methods and the correct contact time.
Complete any local QA checks (self‑tests or logs) required by your organisation.
Technique mistakes during scanning
Mistake 6: Incorrect probe placement or angle
Placing the probe too high or too low, or angling incorrectly, may miss the bladder or include other structures. The pubic bone can also obscure the view if the probe is positioned too low.
How to avoid it:
Place the probe midline just above the pubic symphysis and angle slightly posteriorly as per device guidance.
Make small adjustments rather than large sweeps; re‑centre and repeat if the reading is unexpected.
If the patient cannot lie flat, document the position and interpret results with added caution.
Mistake 7: Using excessive pressure or an unstable hand
Too much pressure can distort anatomy, cause discomfort, and make the probe slide off the optimal plane. Unstable hand position can also lead to ‘rocking’ that changes the scan plane during measurement.
How to avoid it:
Use generous gel and gentle, steady pressure.
Stabilise your hand (resting the ulnar edge if appropriate) and avoid rocking the probe during measurement.
If the abdomen is tender (post‑op, trauma), adapt technique and escalate if scanning is not tolerated.
Mistake 8: Relying on a single reading when results look wrong
Outliers happen due to movement, bowel gas, or targeting error. One number should not drive high‑stakes decisions when the result does not match the clinical picture.
How to avoid it:
Repeat the scan (often two measurements) and confirm the bladder is centred in the targeting guide/image preview.
If repeated readings vary widely, reassess positioning, settings, and technique before acting.
Escalate for senior review or formal imaging if uncertainty remains and the decision carries meaningful risk.
BladderView M5 provides a new and innovative way of bladder scan. It turns the scanning into a fluid Point and Click process. Powered by advanced technology, M5 ensures an easy, quick and precise scanning experience. BladderView M5 is a 3D ultrasound bladder volume instrument used to measure bladder volume and bladder wall thickness non-invasively. The major components of the system are a probe and console which features a touch screen. Bladder volume and ultrasonic images are displayed on the touch screen. An in-built printer and medical cart are also part of the system.
Mistake 9: Mistaking other fluid for bladder volume
Ascites, pelvic cysts, a distended uterus or fluid‑filled bowel can be misread as bladder volume, particularly in complex anatomy. This risk increases when patients cannot lie flat, when bowel gas is significant, or when there is known pelvic pathology.
How to avoid it:
Interpret results alongside history (pregnancy, pelvic masses, known ascites) and the clinical picture.
If readings are unexpectedly high or low, re‑scan with minor repositioning and consider alternative assessment.
When high‑stakes decisions are required, escalate for senior review and consider formal ultrasound.
Interpretation and decision‑making mistakes
Mistake 10: Treating thresholds as universal
There is no single PVR or bladder volume cut‑off that applies to every patient. Thresholds vary by setting, symptoms, comorbidities and local pathways. For example, an asymptomatic patient with a modest residual may be managed differently from a patient in pain and unable to void.
How to avoid it:
Use your organisation’s protocol for escalation and catheterisation decisions.
Consider symptoms, trend over time, and risk factors (for example recent surgery, neurological disease, medications that can contribute to retention).
When the scan conflicts with the clinical picture, repeat the scan and reassess before acting.
Mistake 11: Ignoring confounders that reduce accuracy
Obesity, pelvic organ prolapse, enlarged prostate, abdominal dressings and inability to lie flat can affect readings. Medication effects (for example anticholinergics and opioids) and constipation may contribute to retention and should be considered in assessment.
How to avoid it:
Document confounders and keep technique consistent for repeat monitoring.
If the reading is borderline and the patient is stable, consider repeating after repositioning or after a supervised void.
Escalate when uncertainty remains and the decision is high‑risk.
Troubleshooting difficult scans (practical tips)
Some patients are harder to scan due to body habitus, contractures, dressings, or bowel gas. Use these steps to improve success:
Obesity or deep pelvis: apply more gel, keep the probe steady, and make small angle adjustments rather than large movements.
Bowel gas: adjust angle slightly, pause for patient relaxation, and repeat; consider a brief reposition if tolerated.
Limited mobility/contractures: scan in the safest available position, document it, and maintain consistency for trends.
Dressings/wounds: avoid compromised skin; if scanning is not feasible without risk, escalate for alternative assessment.
Older adult considerations
In nursing homes and geriatric settings, urinary issues often occur alongside delirium, immobility, dehydration, constipation and polypharmacy. Symptoms may be non‑specific, and cooperation may fluctuate. Ensure comfort, communicate calmly, and allow time for the patient to settle before scanning. When retention is suspected, consider reversible contributors such as constipation and medication effects, and involve senior review when needed.
Documentation mistakes
Mistake 12: Recording a number without context
Poor documentation makes it hard for others to interpret results, compare trends, or understand why an action was taken. Good documentation also supports audit and competency review.
How to avoid it:
Record indication, timing relative to voiding, patient position, preset/mode and measured volume (including repeats).
Document symptoms and the action taken (repeat scan, encourage void, escalate, catheterise, monitor).
If monitoring PVR, record the time since void and whether the void was spontaneous or assisted.
Infection prevention mistakes
Mistake 13: Inconsistent cleaning and gel handling
Although scanning is non‑invasive, the probe contacts skin and gel. Inconsistent cleaning increases contamination risk and can damage equipment if incorrect products are used.
How to avoid it:
Use manufacturer‑approved cleaning/disinfection products and correct contact times.
Store devices in a clean area and maintain a clear clean/dirty workflow in busy clinical settings.
Follow local policy for gel use (including single‑use gel where required).
Training and quality assurance mistakes
Mistake 14: Assuming competency after minimal training
Bladder scanning is operator‑dependent. Without supervised practice and refreshers, technique can drift and error rates rise, particularly when scanning is infrequent.
How to avoid it:
Use a competency pathway (theory + supervised scans + sign‑off).
Schedule refreshers and re‑assessment when staff rotate, devices change, or scanning is infrequent.
Use audit/feedback to identify recurring technique issues and target training.
A quick bedside checklist
Use this checklist to reduce avoidable errors:
Confirm indication and timing (especially for PVR).
Position consistently and select the correct preset/mode.
Probe midline above pubic symphysis; gentle pressure; stable hand.
Repeat if results are unexpected; consider confounders.
Document indication, timing, position, volume and action.
Clean/disinfect probe and device per manufacturer guidance.
When to escalate
Escalate when scan results do not fit the clinical picture or when decisions are high‑risk. Examples include severe symptoms with a low measured volume, very high readings after recent voiding, repeated large volumes with renal concerns, or inability to obtain a reliable reading after multiple attempts. In these cases, senior clinical review and/or formal ultrasound may be appropriate.
Conclusion
Most bladder scanning mistakes are preventable with clear indications, correct timing, careful technique and disciplined documentation. Repeat doubtful readings, interpret results in context, and escalate when the numbers do not match the patient’s symptoms. Consistent training and a simple bedside checklist help standardise practice and improve bladder scan accuracy across teams.
