Urinary retention means the bladder does not empty properly. It may present as a sudden inability to pass urine (acute urinary retention) or as ongoing incomplete emptying that can develop gradually (chronic urinary retention). Because retention can lead to urinary tract infection, bladder overdistension and, in some cases, kidney damage, prompt assessment and accurate diagnosis are important.
In clinical practice, the cornerstone of urinary retention diagnosis is measuring how much urine remains in the bladder after voiding. This is called the post-void residual (PVR). A non-invasive bladder scan (bedside ultrasound) is widely used to estimate PVR and support decisions about further testing and treatment.
Key takeaways
Urinary retention may be acute (sudden inability to void) or chronic (ongoing incomplete emptying).
Urinary retention diagnosis relies on clinical assessment plus measurement of post-void residual (PVR).
A bladder scan for urinary retention is a non-invasive way to estimate PVR and is widely used when performed by trained staff.
There is no universal PVR threshold; interpretation must consider age, symptoms and complication risk.
Further tests help identify the cause and guide safe management.
Key definitions: acute vs chronic urinary retention
Clinicians often describe retention by onset and duration:
- Acute urinary retention: a sudden (often painful) inability to pass urine. It typically needs urgent bladder decompression with catheterisation.
- Chronic urinary retention: persistent incomplete emptying with an elevated PVR. It may be painless and can present with frequency, overflow incontinence, recurrent UTIs or renal impairment.
There is no single universally accepted PVR threshold that defines urinary retention in every person. However, very low residual volumes are usually reassuring, while persistently large residual volumes (often described as above about 200–300 mL) suggest significant voiding dysfunction and warrant evaluation in clinical context.
Common causes of urinary retention
Urinary retention is a sign with many possible causes. More than one factor is common, especially in older adults. Major categories include:
- Bladder outlet obstruction (for example, benign prostatic hyperplasia, urethral stricture, pelvic organ prolapse, constipation/fecal impaction).
- Detrusor underactivity or impaired bladder contractility (for example, diabetic autonomic neuropathy, aging-related underactivity).
- Neurologic causes (for example, spinal cord disease/injury, multiple sclerosis, Parkinson disease, stroke, cauda equina syndrome).
- Medication and situational factors (particularly medicines with anticholinergic effects, opioids/sedatives, and postoperative urinary retention).
- Inflammation, infection or mass effects (for example, prostatitis, urethral swelling, pelvic masses).
Symptoms and clinical signs
Symptoms vary with the speed of onset and the degree of incomplete emptying. Acute retention often causes suprapubic pain and a strong urge to avoid it with inability to pass urine. Chronic retention may be painless and less obvious.
Common features include hesitancy, weak stream, straining, prolonged voiding, a sensation of incomplete emptying, frequency/nocturia, suprapubic fullness, and sometimes overflow incontinence.
Why accurate diagnosis matters
Untreated retention can increase the risk of urinary tract infection and discomfort. Long-standing retention can increase bladder pressure and may contribute to upper urinary tract dilation (hydronephrosis) and reduced kidney function in some patients. Diagnosis aims to confirm retention, assess severity and identify the underlying cause.
Urinary retention diagnosis: the clinical assessment pathway
A structured approach helps clinicians confirm retention and decide what to do next.
Step 1: Identify urgency and red flags
Acute urinary retention is usually a medical emergency. Urgent review is warranted if the patient cannot pass urine, is in severe pain, is systemically unwell, or has features suggesting neurologic compromise or renal injury.
Fever/rigors or suspected urosepsis
Visible hematuria (especially with clots)
New lower-limb weakness, saddle anesthesia or severe back pain (possible cauda equina syndrome)
Known or suspected acute kidney injury
Step 2: Focused history
History should clarify onset (sudden vs gradual), voiding symptoms, previous retention episodes, recent surgery/anaesthesia, constipation, fluid intake, and medication exposure (including over-the-counter anticholinergic agents). Ask about neurologic symptoms and conditions such as diabetes or spinal disease.
Step 3: Examination
Examination typically includes abdominal assessment for suprapubic distension/tenderness, a genital and pelvic exam as appropriate, digital rectal exam in men (including assessment for fecal impaction), and a focused neurologic screen when a neurologic cause is suspected.
Bladder scan for urinary retention: measuring post-void residual (PVR)
Measuring PVR is central to diagnosing incomplete bladder emptying. PVR can be measured by urethral catheterisation (the traditional reference standard) or estimated with ultrasound. International teaching resources and guideline statements generally prefer ultrasound bladder volume measurement because it is non-invasive and avoids catheter-related discomfort, trauma and infection risk—provided staff are trained and results are interpreted appropriately.
When a bladder scan is useful
Suspected retention when a patient cannot void
Suspected incomplete emptying (frequency with small voided volumes, weak stream, overflow incontinence)
Post-void residual measurement as part of lower urinary tract symptom assessment (often alongside uroflowmetry in specialist settings)
Monitoring patients at risk of postoperative urinary retention, including after catheter removal, following local protocols
Technique: how to improve reliability
To reduce misleading results, measure PVR as soon as possible after voiding and note whether the void was typical for the patient. Follow device instructions for probe placement. Consider confirmatory catheterisation if the scan result conflicts with symptoms or exam findings.
Accuracy can be reduced by factors such as abdominal ascites, pelvic masses, pregnancy or severe obesity, which may cause false high or low readings depending on anatomy and device algorithms.
How to interpret PVR results
PVR is not interpreted in isolation. One widely cited clinical reference notes that a PVR under 50 mL is normal, and under 100 mL may be acceptable in adults over 65, though higher values are generally considered abnormal—particularly in younger patients. Other teaching modules emphasise that no universally accepted ‘significant’ PVR threshold exists.
As a practical clinical concept, persistently elevated PVR (for example, above about 200–300 mL) may indicate marked bladder dysfunction and can be clinically important, especially when associated with symptoms, recurrent infections or upper urinary tract changes. For non-neurogenic chronic urinary retention, an American Urological Association (AUA) consensus definition uses a PVR greater than 300 mL that persists for at least 6 months and is documented on two or more separate occasions.
Additional tests used to diagnose the cause and assess complications
Once retention is suspected or confirmed, clinicians select further tests based on the situation and likely cause:
Urinalysis (and culture when infection is suspected) to look for UTI or hematuria.
Renal function tests when retention is significant, prolonged, or there is concern for obstructive uropathy.
Ultrasound of kidneys/urinary tract if chronic retention is suspected or renal impairment/hydronephrosis is a concern.
Uroflowmetry plus PVR in specialist assessment of lower urinary tract symptoms.
Urodynamics or cystoscopy in selected cases (for example, when the diagnosis is unclear or when results will change management).
Diagnosing urinary retention in older adults
Older adults are at higher risk because of benign prostatic enlargement, neurologic disease, diabetes, reduced mobility and polypharmacy. Symptoms may be non-specific and pain may be absent in chronic retention. In this population, bladder scanning helps identify clinically significant incomplete emptying while reducing unnecessary catheterisation.
When interpreting PVR in older adults, clinicians often weigh symptoms and risk factors for harm (for example, recurrent UTIs, hydronephrosis or renal impairment) rather than relying on a single number alone.
Medical content notice: This article is for educational information and does not replace individual clinical assessment or local protocols. Anyone unable to pass urine or experiencing severe symptoms should seek urgent medical care.
