Key Facts

Urinary retention is common in older men and can cause significant morbidity if unrecognised. High-pressure chronic retention is a medical emergency due to the risk of renal failure.

Epidemiology

• Lifetime incidence: 10% of men by age 70, 30% by age 80
• Much less common in women
• BPH is present in 50% of men aged 50 and 80% by age 80

Aetiology

Men:

• BPH (most common), prostate cancer, urethral stricture, phimosis Women:
• Pelvic organ prolapse, gynaecological malignancy, urethral stricture Both sexes:
• Constipation, drugs (anticholinergics, opioids, sympathomimetics, antihistamines)
• Neurological: cauda equina syndrome, MS, spinal cord injury, diabetic neuropathy
• Post-surgical (especially pelvic/spinal surgery)
• Blood clot retention (post-haematuria)

Pathophysiology

• Acute: sudden increase in bladder outlet resistance or loss of detrusor function
• Chronic low-pressure: detrusor failure → progressive bladder distension with low intravesical pressure; renal function preserved
• Chronic high-pressure: outflow obstruction with raised intravesical pressure → transmitted to upper tracts → bilateral hydronephrosis → AKI/CKD

Acute Retention

• Sudden inability to pass urine with increasing urgency
• Suprapubic pain (severe, often described as unbearable)
• Palpable/percussable bladder (tender)
• Distress and agitation
• May be precipitated by: anaesthesia, opioids, anticholinergics, alcohol, UTI, constipation

Chronic Retention

• Painless progressive difficulty voiding
• Overflow incontinence (constant dribbling)
• Large palpable bladder (may extend to umbilicus or beyond)
• Nocturia, poor stream, incomplete emptying

High-Pressure Chronic Retention

• Bilateral hydronephrosis
• Renal impairment (raised creatinine)
• Peripheral oedema (fluid overload)
• Post-obstructive diuresis risk after catheterisation

Red Flags

• Bilateral loin pain + renal impairment → high-pressure chronic retention
• Bilateral leg weakness, saddle anaesthesia, loss of anal tone → cauda equina syndrome (neurosurgical emergency)
• Post-obstructive diuresis >200mL/hr → requires IV fluid replacement

Bedside

• Bladder scan: post-void residual volume; >300mL significant, >1000mL chronic retention
• DRE: prostate size (BPH), nodularity/hardness (malignancy)
• Neurological examination: perineal sensation (S2-S4), anal tone, lower limb neurology (cauda equina)

Bloods

• U&Es: renal function (AKI from obstructive uropathy)
• PSA: after DRE (or before, as DRE can falsely elevate); prostate cancer screening
• FBC: anaemia of chronic disease
• Calcium: hypercalcaemia can cause retention

Imaging

• Renal USS: hydronephrosis, kidney size (bilateral hydronephrosis in high-pressure retention)
• MRI spine: if cauda equina suspected (EMERGENCY)
• Transrectal USS/MRI prostate: staging if prostate cancer suspected

Special Tests

• Urodynamic studies: flow rate, detrusor pressure; differentiates obstruction from detrusor failure
• Flexible cystoscopy: urethral stricture assessment
• IPSS (International Prostate Symptom Score): quantify LUTS severity

Acute Retention

• Immediate urethral catheterisation (12-16Fr Foley catheter)
• If urethral catheter fails: suprapubic catheter insertion
• Record residual volume; send CSU for culture
• Monitor for post-obstructive diuresis: if output >200mL/hr, replace with IV 0.9% NaCl (match output)
• Start tamsulosin 400mcg OD (alpha-blocker) to facilitate TWOC
• TWOC (trial without catheter): after 2-3 days of alpha-blocker; success rate 40-50%

Chronic Retention

• Catheterisation (often gradual decompression preferred to reduce risk of haemorrhage, though evidence is limited)
• Monitor renal function closely after decompression
• Replace post-obstructive diuresis fluids with IV saline
• Urgent urology referral if high-pressure retention with renal impairment

Medical Management (BPH)

• Alpha-blockers: tamsulosin 400mcg OD, alfuzosin 10mg OD (relax smooth muscle)
• 5-alpha reductase inhibitors: finasteride 5mg OD (reduces prostate volume; takes 6 months for effect; reduces PSA by 50%)
• Combination therapy: tamsulosin + finasteride for large prostates (CombAT trial)
• Anticholinergics (solifenacin): only for OAB symptoms, NOT for obstruction

Surgical Management

• TURP (transurethral resection of prostate): gold standard for BPH refractory to medical therapy
• HoLEP (holmium laser enucleation): alternative for large prostates
• TUVP, UroLift, Rezum: newer minimally invasive options
• Clean intermittent self-catheterisation (CISC): for neurogenic bladder/detrusor failure

Referral Criteria

• Acute retention → urology
• Chronic retention with renal impairment → urgent urology + nephrology
• Suspected cauda equina → emergency MRI + neurosurgery
• Failed TWOC → urology for surgical assessment

• TWOC success: 40-50% after first episode with alpha-blocker
• Recurrence after successful TWOC: 50% within 2 years
• TURP: symptom improvement in 85-90%; 10-15% require repeat procedure within 10 years
• High-pressure retention: renal function usually recovers after decompression (if not end-stage)
• Post-obstructive diuresis: usually self-limiting within 48-72 hours
• Long-term catheterisation: associated with increased UTI, encrustation, quality of life impact

Drugs Causing Urinary Retention

IPSS Scoring