Urological emergencies
Acute urinary retention
Overview and approach
Acute retention is inability to empty the bladder and may reflect obstruction, drugs or neurological disease.
- Definition: sudden painful inability to void with a palpable or scan-confirmed full bladder. Most common cause in men is BPH; other causes: urethral stricture, constipation, UTI/prostatitis, drugs (anticholinergics, opioids, alpha-agonists), post-operative/post-anaesthetic retention, neurological (cauda equina, cord compression, MS, diabetic neuropathy)1,4.
- Approach: decompress, find the trigger, decide whether a trial without catheter (TWOC) is appropriate, and plan definitive management if it fails.
- Usually there is an outlet problem already: most patients describe a stream that has been slowing for some time. Acute retention with a normal outlet is uncommon and mostly follows surgery, anaesthesia or urethral injury6.
Causes grouped by site6.
| Site | Examples |
|---|---|
| In the lumen | Clot, stone, tumour, foreign body, posterior urethral valves |
| In the wall | Prostatic enlargement (benign or malignant), stricture, urethritis, meatal ulcer, urethral rupture |
| Outside the wall | Faecal impaction, retroverted gravid uterus, fibroids, ovarian cyst, phimosis or paraphimosis |
| Neurogenic | Post-operative, diabetes, spinal cord injury or disease, MS, pelvic nerve damage after rectal surgery |
| Drugs | Alcohol, anticholinergics, antihistamines, smooth muscle relaxants, some sedatives |
- Chronic retention comes in two types. High-pressure: the outlet is obstructed and the bladder keeps generating pressure, which is transmitted up to the kidneys, causing hydronephrosis and post-renal failure. Low-pressure: the detrusor is weak and floppy, the vesicoureteric junctions stay competent, and the kidneys are spared. Renal impairment in chronic retention means the high-pressure type6,7.
Assessment and clinical features
Painful distension, voiding history, medicines, constipation, infection and neurological symptoms; bladder scan where available.
- Features: suprapubic pain and urge with inability to void; palpable/percussable bladder. Chronic retention is typically painless with overflow incontinence.
- The bladder in acute retention: a tense, tender, dull, rounded mass rising out of the pelvis; pressing on it worsens the urge. Percussion helps when it is too tender to feel. A bladder reaching the umbilicus suggests acute-on-chronic retention6.
- The bladder in chronic retention: large but soft and not tender, and pressing may not cause an urge to void. Leaking urine while asleep (not waking to void) is characteristic of chronic retention with overflow6.
- Leave the DRE for prostate size until after catheterisation: a full bladder pushes the prostate back and makes its size impossible to judge6.
- Ask about: LUTS and previous retention, haematuria, fever/dysuria, constipation, medicines (anticholinergics, opioids, decongestants), recent surgery/catheterisation, back pain, saddle numbness, bowel/sexual dysfunction4.
- Examine: abdomen (bladder), DRE (prostate size, faecal loading, anal tone), external genitalia (phimosis, meatal stenosis), lower limb neurology and perianal sensation.
Differentials and investigations
Assess urine and renal function when indicated; distinguish low urine production from retained urine and assess for cauda equina.
- Differentials: oliguria/anuria (check volume on bladder scan), BPH, urethral stricture, clot retention, urethral injury, constipation, drug-induced, neurogenic bladder, cauda equina syndrome, UTI.
- Tests: bladder scan (volume), urinalysis and culture, U&E/creatinine (post-renal AKI), renal tract ultrasound if high-pressure retention suspected (hydronephrosis); PSA is unreliable during retention/catheterisation.
- Measure the drained volume at initial catheterisation and record it; large volumes (> 1 L) and hydronephrosis predict lower TWOC success2,4.
Management and follow-up
Prompt supervised drainage when appropriate, document volume and monitor significant post-obstructive diuresis; treat the cause and plan trial without catheter.
- Drain: urethral catheter (coude tip if prostatic obstruction; smaller calibre post-TURP); if urethral catheterisation fails, urology for guidewire-assisted or suprapubic catheter1,2,4.
- Monitor urine output and electrolytes after drainage for post-obstructive diuresis, especially after large-volume or chronic retention.
- In chronic retention the drained volume is often several litres and the urine is frequently infected, so send a culture. Recovery of renal function may be incomplete7.
- Outlet surgery works well in high-pressure chronic retention, but in low-pressure retention the weak detrusor often still cannot empty afterwards, and patients should be warned7.
- BPH-related retention: start an alpha blocker before TWOC. Cochrane (9 RCTs): successful TWOC 60% with alpha blocker vs 38% placebo (RR 1.55), and fewer recurrent episodes (RR 0.69). Agents with evidence: alfuzosin 10 mg daily, tamsulosin 0.4 mg daily, silodosin; doxazosin/terazosin not generally preferred in retention because of titration and hypotension1,2,3. Ask about planned cataract surgery (floppy iris syndrome) before starting2.
- TWOC timing: no consensus; commonly after 2-3 days of catheterisation, and not before the alpha blocker has had time to work; avoid prolonged catheterisation (urosepsis, haematuria)1,2,5,4.
- After successful TWOC: recurrence is common (OzEMedicine quotes about 50% within a week); consider alpha blocker plus 5-alpha-reductase inhibitor, medication review and urology follow-up4. If TWOC fails twice, refer for surgery (TURP is the usual definitive option)4,5.
Red flags and clinical pearls
Do not force repeated catheter attempts. Suspected urethral trauma or new saddle/sphincter deficits needs urgent specialist care.
- New back pain with saddle numbness, bowel/bladder dysfunction or leg weakness = cauda equina until proven otherwise; urgent MRI and neurosurgical/spinal advice (see Cauda equina and spinal cord compression under Orthopaedics).
- Blood at the meatus or high-riding prostate after trauma: do not catheterise blindly; urethral injury.
- High-pressure retention with hydronephrosis or raised creatinine usually warrants continued catheter drainage and urology input rather than an early TWOC4.
- Opioid/anticholinergic-triggered or post-operative retention often does well with an early TWOC after removing the trigger4.
- Viva: causes, how to catheterise safely, alpha-blocker evidence, why TWOC fails, post-obstructive diuresis.
References
- StatPearls: Male Urinary Retention - Acute and Chronic
- Management guidelines for acute urinary retention (Advisory, 2018)
- Cochrane: Alpha blocker treatment before catheter removal for acute urinary retention in men
- OzEMedicine: Acute urinary retention
- Systematic review and meta-analysis on management of acute urinary retention (Prostate Cancer Prostatic Dis)
- Burnand KG, Black J, Corbett SA, Thomas WEG, editors. Browse's Introduction to the Symptoms and Signs of Surgical Disease. 5th ed. Boca Raton: CRC Press; 2015. Chapter 17, The kidneys, urinary tract and prostate.
- Burnand KG, Black J, Corbett SA, Thomas WEG, editors. Browse's Introduction to the Investigation and Management of Surgical Disease. Boca Raton: CRC Press; 2010. Chapter 20, The urinary tract.
Last updated from Sen’s notes on 22 October 2026.