What is the most commonly recommended diagnostic test for patients suspected of having acute cholecystitis?

Diagnostic Testing for Acute Cholecystitis

Abdominal ultrasound is the most commonly recommended initial diagnostic test for patients suspected of having acute cholecystitis due to its cost-effectiveness, wide availability, reduced invasiveness, and good accuracy for gallstone disease. 1, 2

Diagnostic Algorithm for Suspected Acute Cholecystitis

First-Line Imaging

• Abdominal Ultrasound
  • Sensitivity: 81-88%, Specificity: 80-83% 1, 2
  • Key findings to evaluate:
    • Presence of gallstones
    • Gallbladder wall thickening (>5mm suggests inflammation)
    • Pericholecystic fluid
    • Gallbladder distention
    • Sonographic Murphy sign (tenderness directly over gallbladder) 2

Second-Line Imaging (if ultrasound is inconclusive)

• Hepatobiliary Iminodiacetic Acid (HIDA) scan
  • Higher sensitivity (97%) and specificity (90%) than ultrasound 2, 3
  • Protocol:
    1. Inject HIDA radiotracer intravenously with patient supine
    2. Obtain imaging up to 60 minutes to assess gallbladder visualization
    3. Administer morphine (0.04 mg/kg IV) if gallbladder not visualized by 60 minutes
    4. Continue imaging for additional 30 minutes after morphine 2

Alternative Imaging Options

• CT with IV contrast

  • Useful for evaluating complications or alternative diagnoses
  • More sensitive than ultrasound in some studies (92% vs 79%) 4
  • Particularly valuable in patients without typical clinical signs 2

• Magnetic Resonance Cholangiopancreatography (MRCP)

  • Sensitivity: 85%, Specificity: 81% for cholecystitis
  • Helpful for visualizing hepatic and biliary abnormalities not characterized on ultrasound 2

Clinical Pearls and Pitfalls

Important Considerations

• The absence of a positive Murphy sign does not rule out gallbladder disease, particularly if the patient has received pain medication or has gangrenous cholecystitis 2
• Ultrasound has excellent accuracy (96%) for detecting gallstones but is less accurate for diagnosing acute inflammation 2, 5
• Bedside ultrasound with sonographic Murphy's sign has a 92.2% positive predictive value for acute cholecystitis 6

Common Pitfalls

• Misinterpretation of ultrasound findings: Polyps, sludge, and gallbladder wall thickening can be mistaken for stones or inflammation 6
• Over-reliance on a single test: While ultrasound is the recommended first-line test, it may miss some cases of acute cholecystitis
• Delayed diagnosis: Early diagnosis is essential to prevent potentially life-threatening complications such as cholangitis, pancreatitis, or gallbladder perforation 2

Special Populations

• In older patients, atypical patients, or those with medical comorbidities, consider lower threshold for additional imaging beyond ultrasound 4
• In critically ill patients with suspected acalculous cholecystitis (5-10% of cases), imaging workup may need to be more extensive 3

While some older studies suggested HIDA scan as the first diagnostic modality 7, current guidelines from the World Society of Emergency Surgery (2020) and American College of Radiology strongly recommend ultrasound as the initial imaging test for suspected acute cholecystitis, with additional testing reserved for inconclusive cases 1, 2.