Urinary Retention

Urinary retention can be acute or chronic. When acute it occurs within a number of hours causing significant pain. In contrast, chronic retention is painless and accumulates over weeks to months following an inability to completely empty the bladder after voiding.

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How much is too much?

A bladder volume of >300mls on a bladder scan would justify catheterisation but if a patient is symptomatic with less than this volume then catheterisation must be considered as bladder scans may not always be accurate, e.g in obese patients, pregnancy or ascites.

What to do when the nurse calls?

Ensure you ask the nursing staff to perform a bladder scan, a simple ultrasound device which nurses can use to quantify the amount of fluid. If above 300ml, do ask the nursing staff to encourage voiding with a repeat bladder scan post-void. If the patient is in significant pain, it is often worth asking the nursing staff to immediately catheterise the patient.

Consider the causes whilst progressing through your assessment.


The most common cause of urinary retention is benign prostate hypertrophy (BPH) which can lead to both acute and chronic retention of urine. Patients may already have known BPH or may give a history suggestive of this such as increased urinary frequency, incomplete voiding, hesitancy, nocturia or terminal dribbling.

  • Benign prostatic obstruction
  • Constipation (very common in geriatric patients)
  • Alcohol excess
  • Post-op
  • UTI
  • Postpartum
  • Drugs – antimuscarinic drugs, sympathomimetics, tricyclic antidepressants
  • Bladder stones
  • Detrusor inactivity
  • Neurogenic causes – MS
  • Pelvic surgery
  • Abnormal anatomy -urethral stricture, prostate cancer, BPH

How to recognise


Ask if the patient is in pain? Do they have an urge to empty their bladder? Have they had symptoms of bladder outflow obstruction previously?

  • Can I feel a palpable, distended or percussible bladder? 
  • PR – enlarged or irregular prostate? Any faecal impaction?
  • Bloods – it’s important to check the renal function and inflammatory markers
  • Bladder scan (not necessary if clinically has a distended bladder)


  • The first step is usually to catheterise, particularly in acute retention! It provides instant relief of pain.
  • If retention is due to BPH then an alpha-blocker can be started prior to a trial without a catheter
  • Patients may be referred to Urology for consideration of a transrectal resection of the prostate.
  • Looking for a cause of retention can help prevent future episodes – e.g stopping culprit medications, laxatives for constipation

Complications of urinary retention

  • Renal failure 
  • UTI 
  • Post decompression haematuria 
  • Pathological diuresis – urine output of >200ml/hour or postural hypotension (drop of 20mmHg)
  • Electrolyte abnormalities

References & Further Reading

Dr Emma-James Garden​ (FY3)
Edits by Dr Akash Doshi (CT2)

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