What is the diagnosis for a post-void residual volume of 72 ml on KUB (Kidney, Ureter, and Bladder) ultrasound?

Diagnosis: Incomplete Bladder Emptying with Minimal Voiding Efficiency

This patient has significant incomplete bladder emptying with only 22 ml voided (10% bladder emptying efficiency) and a post-void residual (PVR) of 199 ml, indicating either detrusor underactivity, bladder outlet obstruction, or both—and bethanechol should NOT be given as it has not been demonstrated to be effective for underactive detrusor function. 1

Understanding the Clinical Picture

Your patient's voiding parameters reveal:

• Pre-void volume: 221 ml
• Post-void volume: 199 ml
• Actual voided volume: Only 22 ml
• Voiding efficiency: 10% (severely impaired)

This PVR of 199 ml falls into a clinically significant range, as PVR volumes >200-300 ml indicate significant bladder dysfunction and predict less favorable treatment response. 2, 3 While this patient is just below the 200 ml threshold, the extremely poor voiding efficiency (only 10%) is the critical finding.

Why Bethanechol is NOT Recommended

Muscarinic and cholinergic agonists like bethanechol have not been demonstrated to be effective in the treatment of underactive detrusor function. 1 The guideline from the International Children's Continence Society explicitly states that while anticholinergic agents are effective for detrusor overactivity, cholinergic agonists have failed to show benefit for detrusor underactivity. 1

Additionally, bladder-oriented therapy with cholinergic agents has limited value in patients with incomplete emptying. 4

Differential Diagnosis to Consider

The extremely poor voiding efficiency suggests one of three primary mechanisms:

1. Detrusor Underactivity/Acontractile Bladder

• Characterized by impaired detrusor contractility where the bladder cannot generate adequate pressure to empty 1
• May present with infrequent voiding (once or twice daily), dampness rather than soaking, and impaired bladder sensation 1
• Risk factors include neurologic conditions (diabetes, stroke, spinal cord lesions) 5, 6

2. Bladder Outlet Obstruction

• In men: benign prostatic hyperplasia, urethral stricture 1, 6
• In women: pelvic organ prolapse, urethral stenosis, prior anti-incontinence surgery 1, 5
• Urethral stricture should be in the differential for patients with decreased urinary stream, incomplete emptying, and rising PVR 1

3. Detrusor-Sphincter Dyssynergia

• Inappropriate sphincter contraction during voiding attempt 1, 4
• More common with neurologic conditions 4

Essential Diagnostic Workup

Due to marked intra-individual variability, PVR measurement should be repeated 2-3 times to confirm this finding is truly significant. 2, 3

History Elements to Obtain:

• Neurologic history: stroke, diabetes with neuropathy, multiple sclerosis, spinal cord injury, or other conditions affecting bladder innervation 2, 5, 6
• Medication review: anticholinergics, alpha-adrenergic agonists, opioids 6
• Voiding pattern: frequency of spontaneous voiding, sensation of bladder fullness 1
• In men: symptoms of prostate enlargement, history of urethral instrumentation 1
• In women: history of pelvic surgery, anti-incontinence procedures, obstetric trauma 1, 5

Physical Examination:

• Focused neurologic examination of lower extremities and perineal sensation 2
• In men: digital rectal exam for prostate size/nodules 3
• In women: pelvic examination for prolapse, urethral abnormalities 5

Recommended Testing:

• Uroflowmetry to assess flow pattern and maximum flow rate 1
• Urinalysis and urine culture to rule out infection 5, 6
• Renal ultrasound to assess for hydronephrosis (upper tract protection) 1, 2
• If neurologic disease present or suspected: proceed directly to urodynamic studies with EMG to diagnose detrusor-sphincter dyssynergia and determine bladder pressures 2, 4
• In men with suspected obstruction: consider cystoscopy, retrograde urethrography if urethral stricture suspected 1

Recommended Management Approach

Immediate Management:

Initiate clean intermittent self-catheterization (CISC) every 4-6 hours to prevent bladder filling beyond 500 ml and reduce urinary tract infection risk. 2, 4 This is the first-line intervention for PVR >100 ml with poor voiding efficiency. 2

Additional Conservative Measures:

• Implement a regular moderate drinking and voiding regimen with scheduled voiding attempts every 3-4 hours 1
• Double voiding technique: have patient attempt to void, wait 1-2 minutes, then attempt again—particularly useful in morning and evening 1, 2
• Optimize voiding posture to facilitate pelvic floor relaxation 1
• Address constipation if present, as treating constipation alone improved bladder emptying in 66% of patients with elevated PVR 1, 2

Pharmacologic Considerations:

Alpha-adrenergic antagonists (alpha-blockers) may facilitate bladder emptying by targeting the bladder outlet if there is evidence of bladder outlet obstruction or detrusor-sphincter dyssynergia. 1, 4 However, these should only be initiated after determining the underlying mechanism through appropriate testing.

Avoid antimuscarinic medications (used for overactive bladder) in this patient, as they are contraindicated with PVR approaching 200 ml. 2

Monitoring and Follow-up

• Repeat PVR measurement 4-6 weeks after initiating treatment to assess response 2
• Monitor for urinary tract infections, as incomplete emptying significantly increases infection risk 1
• Regular voiding charts and flow rate recordings to track improvement 1

Critical Pitfalls to Avoid

• Do not prescribe bethanechol or other cholinergic agonists—they lack efficacy for detrusor underactivity 1, 4
• Do not base treatment decisions on a single PVR measurement—always confirm with repeat testing 2, 3
• Do not assume elevated PVR alone indicates obstruction—it cannot differentiate between obstruction and detrusor underactivity without urodynamics 2
• Do not use indwelling catheters when intermittent catheterization is feasible, as indwelling catheters increase UTI risk 2, 4
• Do not delay evaluation in patients with neurologic conditions—they require urgent assessment to prevent upper tract damage 2