What to do if a patient has urinary retention with a bladder scan showing no urine volume?

Anuria with Empty Bladder (0mL on Bladder Scan)

Immediate Assessment: This is NOT Urinary Retention

When a patient is not urinating AND bladder scan shows 0mL, this represents anuria (absence of urine production) rather than urinary retention (inability to void despite urine in the bladder). This is a fundamentally different clinical scenario requiring urgent evaluation for renal failure or complete urinary tract obstruction above the bladder level 1, 2.

Critical Distinction

• Urinary retention: Bladder scan shows >100-300mL of urine that cannot be voided 1, 2, 3
• Anuria with empty bladder: Bladder scan shows 0mL, indicating either:
  • Acute kidney injury/failure (kidneys not producing urine)
  • Complete bilateral ureteral obstruction (urine cannot reach bladder)
  • Severe prerenal azotemia (inadequate renal perfusion)

Immediate Diagnostic Workup

Step 1: Assess Volume Status and Hemodynamics

• Check vital signs including blood pressure, heart rate, and orthostatic changes 1
• Evaluate for signs of volume depletion: dry mucous membranes, decreased skin turgor, tachycardia 1
• Assess for fluid overload: peripheral edema, pulmonary crackles, jugular venous distension 1

Step 2: Obtain Urgent Laboratory Studies

• Serum creatinine and blood urea nitrogen to assess renal function 1
• Electrolytes (particularly potassium, which can be life-threatening if elevated) 1
• Urinalysis if any urine can be obtained 4, 3
• Complete blood count to evaluate for infection or anemia 3

Step 3: Imaging to Identify Obstruction

• Renal ultrasound is the first-line imaging modality to assess for hydronephrosis (indicating ureteral obstruction) and measure kidney size 1, 2
• Scan both kidneys systematically from top to bottom in transverse and sagittal planes 2
• CT abdomen/pelvis without contrast if ultrasound is nondiagnostic or if body habitus limits visualization 1
• Avoid IV contrast initially given concern for acute kidney injury 1

Step 4: Review Medication History

• Identify nephrotoxic medications: NSAIDs, ACE inhibitors, ARBs, aminoglycosides 1, 5
• Note drugs that can cause urinary retention if catheterization reveals retained urine: anticholinergics, opioids, alpha-agonists 5, 3

Management Algorithm Based on Findings

If Bilateral Hydronephrosis Present (Ureteral Obstruction)

• Urgent urology consultation for bilateral ureteral stent placement or percutaneous nephrostomy 1
• This represents a urologic emergency requiring immediate intervention 6
• Common causes: bilateral ureteral stones, retroperitoneal fibrosis, pelvic malignancy 1

If No Hydronephrosis (Intrinsic Renal Failure or Prerenal Azotemia)

• Assess volume status to differentiate prerenal from intrinsic renal causes 1
• If hypovolemic: Initiate IV fluid resuscitation with isotonic crystalloid and monitor urine output response 1
• If euvolemic or hypervolemic: Consider intrinsic acute kidney injury and nephrology consultation 1
• Monitor for complications of acute kidney injury: hyperkalemia, metabolic acidosis, uremia 1

If Small Kidneys on Ultrasound

• Suggests chronic kidney disease with acute-on-chronic renal failure 1
• Nephrology consultation for potential dialysis initiation 1
• Assess for uremic symptoms: altered mental status, pericarditis, bleeding 1

Common Pitfalls to Avoid

• Do not assume urinary retention when bladder scan shows 0mL—this requires evaluation for renal failure or upper tract obstruction 1, 2
• Do not place a urinary catheter expecting to drain urine when bladder scan is 0mL—there is no urine to drain 1
• Do not delay imaging in patients with anuria, as bilateral ureteral obstruction requires urgent decompression 1
• Do not administer IV contrast for CT imaging until renal function is assessed, as this can worsen acute kidney injury 1
• Do not overlook medication-induced causes: NSAIDs and ACE inhibitors can precipitate acute kidney injury, particularly in volume-depleted patients 1, 5

Special Populations

Elderly Patients

• Higher risk for acute kidney injury from multiple medications and comorbidities 7
• May have baseline chronic kidney disease making them more susceptible to acute insults 7
• Consider fecal impaction as a cause of bilateral ureteral compression in bedridden patients 7

Post-Surgical Patients

• Anuria may result from intraoperative hypotension, nephrotoxic anesthetics, or inadvertent ureteral injury 5
• Review operative notes for proximity of surgery to ureters 1

Patients with Neurogenic Bladder

• Empty bladder on scan does not rule out upper tract obstruction from chronic high-pressure voiding 1, 2
• These patients require urodynamic evaluation and upper tract imaging 2

Disposition and Follow-Up

• Admit patients with acute kidney injury, bilateral obstruction, or electrolyte abnormalities requiring monitoring 1, 6
• Nephrology consultation for patients with intrinsic renal failure or need for renal replacement therapy 1
• Urology consultation for patients with obstructive uropathy requiring intervention 1, 6