Introduction

Acute urinary retention is when a person suddenly (over a period of hours or less) becomes unable to voluntarily pass urine. It is the most common urological emergency and there are several potential causes that must be investigated for.

Epidemiology

  • Incidence: 200.00 cases per 100,000 person-years
  • Peak incidence: 70+ years
  • Sex ratio: more common in males 10:1
<1 1-5 6+ 16+ 30+ 40+ 50+ 60+ 70+ 80+

Aetiology

Aetiology
  • In men, acute urinary retention most commonly occurs secondary to benign prostatic hyperplasia; a condition where the prostate becomes enlarged but non-cancerous. The enlarged prostate presses on the urethra which can make the bladder wall thicker and less able to empty.
  • Other urethral obstructions; including urethral strictures, calculi, cystocele, constipation or masses.
  • Some medications can cause acute urinary retention by affecting nerve signals to the bladder: these include anticholinergics, tricyclic antidepressants, antihistamines, opioids and benzodiazepines.
  • Less commonly, there may be a neurological cause for the acute urinary retention.
  • In patients with predisposing causes, a simple urinary tract infection can be enough to cause acute urinary retention
  • Acute urinary retention often occurs postoperatively and in women postpartum: usually secondary to a combination of the above risk factors.

Clinical features

Patients typically present with a subacute onset of:
  • Inability to pass urine
  • Lower abdominal discomfort
  • Considerable pain or distress

This differs from chronic urinary retention which is typically painless. In a patient with a background of chronic urinary retention, acute urinary retention may present instead with overflow incontinence.

Signs:
  • Palpable distended urinary bladder either on an abdominal or rectal exam
  • Lower abdominal tenderness
  • All men and women should have a rectal and neurological examination to assess for the likely causes above. Women should also have a pelvic examination.

Investigations

Investigations:
  • Patients should all be investigated with a urine sample which should be sent for urinalysis and culture. This might only be possible after urinary catheterisation.
  • Serum U&Es and creatinine should also be checked to assess for any kidney injury.
  • A FBC and CRP should also be performed to look for infection
  • PSA is not appropriate in acute urinary retention as it is typically elevated

Management

Management
  • To confirm the diagnosis of acute urinary retention a bladder ultrasound should be performed. A volume of >300 cc confirms the diagnosis, but if the history and examination are consistent, with an inconsistent bladder scan, there are causes of bladder scan inaccuracies and hence the patient can still have acute urinary retention.
  • Acute urinary retention is managed by decompressing the bladder via catheterisation
  • Urinary catheterisation can be performed in patients with suspected acute urinary retention, and the volume of urine drained in 15 minutes measured. A volume of <200 confirms that a patient does not have acute urinary retention, and a volume over 400 cc means the catheter should be left in place. In between these volumes, it depends on the case.
  • Further investigation should be targeted by the likely cause. In reversible causes such as UTI, resolution with treatment is sufficient and further investigation is not necessary. Men not diagnosed by BPH should be further evaluated by a urologist, Patients with neurological symptoms should be evaluated by a neurologist and women with gynaecological symptoms by a gynaecologist. Where no likely cause is identified, patients should be evaluated by a urologist for anatomical and urodynamic causes.