What investigations are needed to determine the cause of urinary retention?

Investigations for Urinary Retention

A comprehensive diagnostic approach for urinary retention should include bladder scanning or catheterization to measure post-void residual volume, urinalysis, assessment of prostate size via digital rectal examination, and evaluation of neurological function. 1, 2

Initial Assessment

History and Physical Examination

• Medication review: Focus on anticholinergics, alpha-adrenergic agonists, and opioids 2
• Symptom assessment: Use validated tools like AUA Symptom Index/IPSS to quantify severity 1
• Digital rectal examination: Evaluate prostate size, consistency, and abnormalities 1
• Neurological examination: Assess perineal sensation and lower limb motor/sensory function 1
• Abdominal examination: Check for palpable bladder and suprapubic tenderness 1

First-Line Investigations

1. Post-void residual (PVR) measurement:

   • Bladder scanning (non-invasive) 1
   • Catheterization (when scanner unavailable or results questionable) 1
   • Chronic urinary retention defined as PVR >300 mL on two occasions, persisting ≥6 months 2

2. Urinalysis:

   • Evaluate for hematuria, pyuria, proteinuria, and other abnormalities 1
   • Urine culture if infection is suspected 1

Advanced Investigations

For Suspected Obstructive Causes

1. Prostate-specific antigen (PSA):

   • Indicated when prostate cancer is suspected and when life expectancy >10 years 1
   • Consider PSA density, velocity, and free/total PSA ratio to improve specificity 1

2. Uroflowmetry:

   • Measures maximum urinary flow rate to assess severity of obstruction 1
   • Particularly useful in men with suspected BPH 3

3. Imaging Studies:

   • Transrectal ultrasound: Measures prostate volume 3
   • CT urography or retrograde urethrography: For suspected urethral stricture 1
   • Cystography: For suspected bladder injury 1

For Suspected Neurological Causes

1. Urodynamic studies:

   • Multichannel filling cystometry: Evaluates detrusor function, compliance, and overactivity 1
   • Pressure-flow studies: Assesses for bladder outlet obstruction 1
   • Indicated when invasive treatments are being considered 1

2. Frequency-volume charts:

   • Document time and volume of each void over 3 days 1
   • Particularly useful when nocturia is predominant 1

For Complicated Cases

1. Cystourethroscopy:

   • Direct visualization of urethra and bladder 1
   • Indicated for recurrent retention or when structural abnormality is suspected 1

2. MRI of pelvis/spine:

   • For suspected neurological causes or pelvic organ involvement 1
   • Not typically indicated in acute setting 1

Special Considerations

In Men

• Focus on prostate assessment (BPH accounts for 53% of urinary retention cases) 2
• Consider alpha-blocker therapy at time of catheter insertion to increase chance of successful voiding trial 4

In Women

• Evaluate for pelvic organ prolapse 1
• Consider stress testing with prolapse reduction if high-grade prolapse is present 1

In Elderly Patients

• Assess for constipation, which can contribute to urinary retention 5
• Consider medication review as polypharmacy is common 5

Common Pitfalls to Avoid

• Failing to check for constipation: Severe constipation can cause urinary retention through increased abdominal pressure 5
• Overlooking medication causes: Many commonly prescribed medications can cause or worsen urinary retention 2
• Missing neurological causes: Stroke, multiple sclerosis, and other neurological conditions can affect bladder function 5
• Relying solely on symptoms: The absence of symptoms does not rule out significant urinary retention 1

By following this systematic approach to investigating urinary retention, clinicians can identify the underlying cause and implement appropriate treatment strategies to improve patient outcomes.