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.

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.
Ask about: LUTS and previous retention, haematuria, fever/dysuria, constipation, medicines (anticholinergics, opioids, decongestants), recent surgery/catheterisation, back pain, saddle numbness, bowel/sexual dysfunction (4).
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 success (2)(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 catheter (1)(2)(4).
Monitor urine output and electrolytes after drainage for post-obstructive diuresis, especially after large-volume or chronic retention.
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 hypotension (1)(2)(3). Ask about planned cataract surgery (floppy iris syndrome) before starting (2).
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-up (4). 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 TWOC (4).
Opioid/anticholinergic-triggered or post-operative retention often does well with an early TWOC after removing the trigger (4).
Viva: causes, how to catheterise safely, alpha-blocker evidence, why TWOC fails, post-obstructive diuresis.

References

Last updated from Sen’s notes on 9 October 2026.