Overview
Acute Urinary Retention
1. Clinical Overview
Summary
Acute urinary retention (AUR) is the sudden inability to pass urine despite a full bladder, causing significant distress and suprapubic pain. It is a urological emergency requiring immediate bladder drainage via catheterisation. AUR occurs most commonly in elderly men with benign prostatic hyperplasia (BPH) but has numerous precipitants including medications, constipation, and neurological causes. Identification of the underlying cause and appropriate follow-up with trial without catheter (TWOC) is essential for management.
Key Facts
- Definition: Painful inability to void with palpable/percussable bladder greater than 300ml
- Prevalence: Lifetime risk 10% in men greater than 70 years
- Volume at presentation: Typically 500-800ml retained
- Most common cause (men): Benign prostatic hyperplasia (BPH)
- Key management: Immediate urethral catheterisation
- Critical distinction: Acute (painful) vs Chronic retention (painless, high residual)
Clinical Pearls
The Drug Checklist: Always review medications - anticholinergics, opioids, antihistamines, and sympathomimetics are common precipitants. Stopping the offending drug may prevent recurrence.
Cauda Equina Alert: Any patient with urinary retention plus bilateral leg symptoms or saddle anaesthesia requires emergency MRI spine. Do not wait for other investigations.
The 3Ps of Precipitants: Prostate (BPH/cancer), Pharmacological (drugs), and Poo (constipation) - address all three.
Why This Matters Clinically
AUR causes immediate patient distress and can lead to bladder decompensation if not treated promptly. High-pressure chronic retention can cause bilateral hydronephrosis and irreversible renal damage. Identification of neurological causes (cauda equina) is time-critical for neurological recovery.
2. Epidemiology
Incidence & Prevalence
- Incidence: 2.2 per 1000 men per year aged 40-83
- Cumulative incidence: 10% lifetime risk in men over 70
- Prevalence in women: Much rarer (1:13 female:male ratio)
- Trend: Increasing due to ageing population
Demographics
| Factor | Details |
|---|---|
| Age | Rare before 50; increases exponentially with age |
| Sex | Male:Female ratio 13:1 |
| Ethnicity | Similar across ethnic groups |
| Geography | Higher in developed countries |
Risk Factors
Non-Modifiable:
- Age greater than 60 years
- Male sex
- Previous episode of AUR
- Neurological disease (MS, Parkinson's, spinal cord lesions)
Modifiable:
| Risk Factor | Relative Risk |
|---|---|
| BPH/Large prostate volume | 3-5x |
| Anticholinergic medications | 2-3x |
| Opioid use | 2x |
| Constipation | 1.5-2x |
| Recent surgery/anaesthesia | 2-3x |
3. Pathophysiology
Mechanism
Step 1: Bladder Outlet Obstruction or Detrusor Dysfunction
- Mechanical obstruction (BPH, stricture, tumour)
- OR detrusor underactivity (neurological, drug-induced)
- OR combination of both
Step 2: Progressive Bladder Distension
- Bladder fills but cannot empty
- Intravesical pressure rises
- Bladder wall stretches, causing pain
- Detrusor contractility may be impaired by overdistension
Step 3: Complications of Urinary Stasis
- UTI risk increases
- In chronic high-pressure retention: transmission to upper tracts
- Bilateral hydronephrosis and renal impairment may develop
Step 4: Post-Obstructive Diuresis (after relief)
- Accumulated solutes and water excreted
- Physiological vs pathological diuresis
- Risk of dehydration and electrolyte derangement
Classification
| Type | Definition | Clinical Features |
|---|---|---|
| Acute retention | Sudden, painful, cannot void | Suprapubic pain, distress |
| Chronic retention | Gradual, painless, large residual | Often detected on imaging/catheter |
| Acute-on-chronic | Acute presentation with underlying chronic | Mixed features |
| High-pressure chronic | Back-pressure to kidneys | Bilateral hydronephrosis, raised creatinine |
| Low-pressure chronic | Large residual, no renal impact | Overflow incontinence |
Anatomical Considerations
- Male urethra: 18-22cm; female urethra: 3-4cm
- BPH causes obstruction at prostatic urethra
- Strictures most common at bulbar urethra (post-instrumentation) or meatus (post-BXO)
- In women: pelvic organ prolapse, urethral diverticulum, or pelvic masses cause obstruction
4. Clinical Presentation
Symptoms
Typical Presentation:
Atypical Presentations:
Signs
Red Flags
[!CAUTION] Red Flags — Urgent action required if:
- Bilateral leg weakness or numbness (cauda equina syndrome) — emergency MRI
- Saddle anaesthesia or faecal incontinence (cauda equina) — emergency MRI
- Bilateral hydronephrosis or raised creatinine (high-pressure retention)
- Fever and rigors (urosepsis) — antibiotics and urgent catheterisation
- Post-obstructive diuresis greater than 200ml/hr — fluid and electrolyte monitoring
Sudden inability to void (100%)
Common presentation.
Suprapubic pain and distress (95%)
Common presentation.
Urge to void but cannot (90%)
Common presentation.
Lower abdominal distension (80%)
Common presentation.
5. Clinical Examination
Structured Approach
General:
- Vital signs (sepsis screen)
- Conscious level (confusion in elderly)
- Signs of chronic kidney disease (pallor, oedema)
Abdominal Examination:
- Inspect: Lower abdominal distension
- Palpate: Suprapubic mass arising from pelvis
- Percuss: Dull above pubic symphysis
- Auscultate: Bowel sounds (exclude obstruction)
Digital Rectal Examination (DRE):
- Prostate size, consistency, nodules
- Anal tone (reduced in cauda equina)
- Faecal loading (constipation as precipitant)
Neurological Examination:
- Lower limb power, sensation, reflexes
- Saddle sensation (S2-4)
- Perianal sensation and anal tone
Special Tests
| Test | Technique | Positive Finding | Sensitivity/Specificity |
|---|---|---|---|
| Bladder percussion | Percuss suprapubically | Dull note above pubic bone | 80%/90% |
| Bladder scan | Ultrasound probe suprapubically | Volume greater than 300ml | 95%+ |
| DRE | Digital examination of prostate | Enlarged, nodular, or tender prostate | N/A |
| Neurological exam | Power, sensation, reflexes | Focal deficits, saddle anaesthesia | N/A |
6. Investigations
First-Line (Bedside)
- Bladder scan — Confirm urinary retention (volume greater than 300ml)
- Urinalysis — Exclude UTI or haematuria
- Observations — Exclude sepsis
Laboratory Tests
| Test | Expected Finding | Purpose |
|---|---|---|
| U&Es | May be elevated in high-pressure retention | Assess renal function |
| FBC | WCC elevated if infection | Infection screen |
| PSA | May be elevated in BPH or cancer | Baseline (do NOT measure in acute retention - falsely elevated) |
| Urine culture | Positive if UTI | Guide antibiotic therapy |
Imaging
| Modality | Findings | Indication |
|---|---|---|
| Ultrasound KUB | Bladder volume, hydronephrosis, prostate size | First-line; assess upper tracts |
| CT KUB | Stones, tumour, hydronephrosis | If stone or malignancy suspected |
| MRI Spine | Cord/cauda compression | If neurological cause suspected |
Diagnostic Criteria
- AUR diagnosed by: Painful inability to void + Palpable bladder or Bladder scan greater than 300ml
- Chronic retention: Painless + Residual greater than 1000ml
- High-pressure retention: Chronic retention + Bilateral hydronephrosis + Raised creatinine
7. Management
Management Algorithm
ACUTE URINARY RETENTION
↓
┌─────────────────────────────────────────┐
│ IMMEDIATE ASSESSMENT │
│ Bladder scan, vital signs, neuro exam │
└─────────────────────────────────────────┘
↓
┌─────────────────────────────────────────┐
│ NEUROLOGICAL RED FLAGS? │
├─────────────────────────────────────────┤
│ YES → EMERGENCY MRI SPINE │
│ NO → Continue │
└─────────────────────────────────────────┘
↓
┌─────────────────────────────────────────┐
│ URETHRAL CATHETERISATION │
│ (Record residual volume) │
└─────────────────────────────────────────┘
↓
┌─────────────────────────────────────────┐
│ CATHETER FAILED? │
├─────────────────────────────────────────┤
│ YES → Suprapubic catheter (SPC) │
│ NO → Continue │
└─────────────────────────────────────────┘
↓
┌─────────────────────────────────────────┐
│ ASSESS FOR HIGH-PRESSURE │
│ U&Es, Renal USS │
├─────────────────────────────────────────┤
│ HIGH PRESSURE → Long-term catheter, │
│ Urology referral │
│ LOW PRESSURE → TWOC in 2-3 days │
└─────────────────────────────────────────┘
Acute/Emergency Management
Immediate Actions:
- Confirm diagnosis with bladder scan
- Exclude neurological emergency (cauda equina)
- Insert urethral catheter (12-14F Foley initially)
- Record residual volume
- Send urine for culture if cloudy
- Start alpha-blocker (tamsulosin) if planning TWOC
Conservative Management
- Remove precipitating medications where possible
- Treat constipation
- Address underlying causes (UTI, post-operative pain)
Medical Management
| Drug Class | Drug | Dose | Duration |
|---|---|---|---|
| Alpha-blocker | Tamsulosin | 400mcg OD | Start immediately, continue post-TWOC |
| 5-alpha reductase inhibitor | Finasteride | 5mg OD | Long-term for BPH |
| Antibiotic (if UTI) | Per sensitivities | 7 days | As per culture |
Surgical Management (if applicable)
Indications for Suprapubic Catheter:
- Failed urethral catheterisation
- Urethral stricture
- Urethral trauma
- Patient preference
Procedures:
- TWOC (Trial Without Catheter): Remove catheter after 2-3 days on alpha-blocker; 40-50% success rate
- TURP: Transurethral resection of prostate for BPH
- Urethral dilatation/urethrotomy: For strictures
- Clean intermittent self-catheterisation (CISC): For neurogenic bladder
Disposition
- Admit if: High-pressure retention, post-obstructive diuresis, sepsis, neurological cause suspected
- Discharge if: Successful catheterisation, stable renal function, community nursing for catheter care, TWOC planned
- Follow-up: TWOC in 2-3 days; Urology clinic within 2-4 weeks
8. Complications
Immediate (Minutes-Hours)
| Complication | Incidence | Presentation | Management |
|---|---|---|---|
| Failed catheterisation | 5-10% | Unable to pass urethral catheter | Suprapubic catheter |
| Urethral trauma | 2-5% | Bleeding, false passage | Specialist urology input |
| Vasovagal syncope | 1-2% | On decompression | Lie flat, reassure |
Early (Days)
- Post-obstructive diuresis: Greater than 200ml/hr urine output — IV fluids, electrolyte monitoring
- Catheter-associated UTI: 3-5% per day — Antibiotics per sensitivities
- Haematuria (ex vacuo): Bleeding from decompression — Usually self-limiting
Late (Weeks-Months)
- Recurrent retention: 50-60% if underlying cause not treated
- Need for TURP or long-term catheter: 30-40%
- Chronic kidney disease: If high-pressure retention not identified
9. Prognosis & Outcomes
Natural History
- Without treatment: Bladder decompensation, overflow incontinence
- High-pressure retention: Progressive renal impairment
- With treatment: Resolution in 40-50% with TWOC; remainder need intervention
Outcomes with Treatment
| Variable | Outcome |
|---|---|
| TWOC success | 40-50% first attempt |
| TWOC success with alpha-blocker | 50-60% |
| Long-term catheter rate | 10-15% |
| TURP success | 80-90% resolution |
Prognostic Factors
Good Prognosis:
- First episode
- Identifiable precipitant (drugs, constipation)
- Small prostate volume
- Successful TWOC
Poor Prognosis:
- Previous episodes
- Large residual volume (greater than 1L)
- Large prostate volume
- Neurological cause
- High-pressure chronic retention
10. Evidence & Guidelines
Key Guidelines
- NICE CKS Urinary Retention — Clinical Knowledge Summary. NICE CKS
- EAU Guidelines on Non-Neurogenic Male LUTS (2023) — Management of BPH and urinary retention. EAU
- BAUS Guidelines — British Association of Urological Surgeons acute retention pathway.
Landmark Trials
ALFAUR Study (2008) — Alfuzosin in acute urinary retention
- 357 patients randomised
- Key finding: Alfuzosin increased successful TWOC from 29% to 62%
- Clinical Impact: Alpha-blockers now standard before TWOC
REDUCE Study (2010) — Dutasteride in men with enlarged prostate
- 6729 men with BPH
- Key finding: Dutasteride reduced AUR risk by 57% over 4 years
- Clinical Impact: 5-alpha reductase inhibitors prevent AUR in high-risk men
Evidence Strength
| Intervention | Level | Key Evidence |
|---|---|---|
| Alpha-blocker before TWOC | 1b | ALFAUR Study |
| 5-ARI for BPH | 1b | REDUCE Trial |
| TURP for refractory retention | 2a | Multiple cohort studies |
| Suprapubic catheter for failed urethral | 2b | Expert consensus |
11. Patient/Layperson Explanation
What is Acute Urinary Retention?
Acute urinary retention (AUR) means you suddenly cannot pass urine, even though your bladder is full. This causes significant pain and discomfort in your lower tummy. Think of it like a blocked drain — the water builds up but cannot flow out.
Why does it matter?
If urine cannot drain, the pressure builds up. This is very painful and distressing. In severe cases, the back-pressure can damage your kidneys. The good news is that draining the bladder with a tube (catheter) relieves the problem quickly.
How is it treated?
- Catheter: A small tube is passed through your urethra (water pipe) into the bladder to drain urine. This gives immediate relief.
- Medication: Tablets (alpha-blockers) help relax the prostate and bladder neck, making it easier to pass urine when we remove the catheter.
- Trial without catheter: After 2-3 days on tablets, we remove the catheter to see if you can pass urine naturally.
- Surgery: If retention keeps happening, an operation to reduce the prostate size may be needed.
What to expect
- A catheter draining your bladder gives immediate relief
- You may go home with a catheter and leg bag
- You will return in 2-3 days to try without the catheter
- About half of men pass urine successfully; others may need further treatment
When to seek help
Go to A&E or call 999 if you:
- Cannot pass urine and have lower tummy pain
- Have a catheter that is blocked or not draining
- Develop fever, confusion, or feel very unwell with a catheter
- Have leg weakness, numbness, or difficulty controlling your bowels
12. References
Primary Guidelines
- McNeill SA. The role of alpha-blockers in the management of acute urinary retention. BJU Int. 2004;93(Suppl 1):27-30. PMID: 14871045
Key Trials
- McNeill SA, et al. Alfuzosin once daily facilitates return to voiding in patients in acute urinary retention. J Urol. 2004;171(6 Pt 1):2316-20. PMID: 15126810
- Roehrborn CG, et al. The effects of dutasteride, tamsulosin and combination therapy on lower urinary tract symptoms in men with benign prostatic hyperplasia and prostatic enlargement. J Urol. 2008;179(2):616-21. PMID: 18082216
- Fitzpatrick JM, et al. Management of acute urinary retention: a worldwide survey of 6074 men with benign prostatic hyperplasia. BJU Int. 2012;109(1):88-95. PMID: 21615852
Further Resources
- NHS Urinary Retention: nhs.uk/conditions/urinary-retention
- Prostate Cancer UK: prostatecanceruk.org
Last Reviewed: 2025-12-24 | MedVellum Editorial Team
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists for emergency situations.