Urinary Retention Diagnosis and Tests

Post-Void Residual (PVR) Measurement

This is the gold standard for confirming diagnosis.

• Ultrasound Bladder Scanner: A non-invasive bedside tool that calculates urine volume using 3D ultrasound. It is quick and painless.
• In-and-Out Catheterization: More accurate but invasive. A small catheter is passed to drain the bladder and measure the volume directly.
• Diagnostic Criteria:
  • PVR < 50 mL: Normal.
  • PVR > 100-200 mL: Suggests abnormal emptying; warrants monitoring.
  • PVR > 300 mL: Diagnosis of Chronic Retention.

Renal Ultrasound

Performed to check the upper urinary tract (kidneys and ureters). We look for Hydronephrosis (swelling of the kidney pelvis) and Hydroureter. This indicates that the bladder pressure is dangerously high and backing up into the kidneys, putting the patient at risk of permanent renal failure. This test is mandatory for men with elevated creatinine levels.

Urodynamics (Pressure-Flow Studies)

This is the definitive functional test, reserved for complex or unclear cases (e.g., distinguishing between obstruction and a weak bladder before surgery).

• The Concept: It simultaneously measures the pressure inside the bladder and the flow rate of urine. It answers the fundamental question: “Is the flow low because the prostate is blocking it (High Pressure/Low Flow), or because the bladder muscle is too weak to push (Low Pressure/Low Flow)?”
• Why it matters: If the bladder muscle is dead (acontractile), removing the prostate (TURP) will not fix the retention. Urodynamics prevents unnecessary surgery and guides appropriate management (e.g., catheterization).

Cystoscopy

A visual inspection of the urethra and bladder using a flexible fiberoptic camera passed through the urethra.

• Utility: It identifies physical blockages such as urethral strictures (scar tissue), bladder neck contractures, large prostate lobes (specifically median lobes) obstructing the channel, bladder stones, or tumors. It helps plan the surgical approach (e.g., laser vs. resection).

Retrograde Urethrogram (RUG)

If a urethral stricture is suspected (e.g., history of trauma or sexually transmitted infection), dye is injected into the urethra and X-rays are taken. This visualizes the location, length, and density of the narrowing to plan reconstruction (Urethroplasty).

Ambulatory Urodynamics

Under challenging cases where standard urodynamics fail to capture the pathology, ambulatory testing allows for natural filling and voiding monitoring over several hours.