What is the diagnostic approach for gallstones?

Diagnosis of Gallstones

Abdominal ultrasound is the first-line diagnostic test for gallstones, with a sensitivity of 84-97% and specificity of 95-99%. 1

Initial Diagnostic Approach

Laboratory Testing

Obtain the following blood tests in all patients with suspected gallstones 1:

• Liver function tests: ALT, AST, alkaline phosphatase, total and direct bilirubin, and GGT 2, 1
• Pancreatic enzymes: Amylase and lipase to exclude pancreatitis as a complication 1

These biochemical tests help stratify risk for common bile duct stones and guide further management 2.

Primary Imaging: Abdominal Ultrasound

Ultrasound is the cornerstone imaging modality and should be performed in all patients with suspected gallstones. 1, 3

Key ultrasound findings to document 2, 1:

• Presence of gallstones: Appear as echogenic structures with posterior acoustic shadowing 2
• Gallbladder wall thickness: >3 mm is abnormal and suggests cholecystitis 2
• Common bile duct diameter: Normal upper limit is approximately 3 mm, though may increase 1 mm per decade of age 2
• Sonographic Murphy sign: Focal tenderness when probe compresses the gallbladder 2

Important caveat: Ultrasound has limited sensitivity (22.5-75%) for detecting common bile duct stones, so a negative ultrasound does not exclude choledocholithiasis 1.

When Ultrasound is Negative or Equivocal

For Suspected Acute Cholecystitis

Obtain a hepatobiliary iminodiacetic acid (HIDA) scan if clinical suspicion remains high despite negative or equivocal ultrasound. 1, 4

• HIDA scan has 97% sensitivity and 90% specificity for acute cholecystitis 1

For Suspected Common Bile Duct Stones

Stratify patients by risk level for choledocholithiasis 2:

High-risk patients (>50% probability) should undergo:

• MRCP (sensitivity 85-100%, specificity 90%) 2, 1
• Endoscopic ultrasound (sensitivity 95%, specificity 97%) 2
• Direct ERCP if stone is visualized on abdominal ultrasound 2

Moderate-risk patients require additional testing 2:

• MRCP or endoscopic ultrasound preoperatively (both have comparable accuracy) 2
• Intraoperative cholangiography or laparoscopic ultrasound (sensitivity 87%, specificity 99-100%) 2

CT Scanning

CT is not first-line for gallstone diagnosis but has specific roles 2:

• CT with IV contrast should be used when ultrasound is equivocal or to evaluate complications (gangrene, perforation, abscess) 2, 1
• CT detects only ~75% of gallstones because many cholesterol stones are not radiopaque 2
• CT without contrast has very limited value for suspected biliary disease 2

Special Populations

In pregnant patients: Use ultrasound or MRI as the initial imaging modality to avoid radiation exposure 1.

In elderly patients: Apply the same diagnostic algorithm, but note that common bile duct diameter normally increases with age 2, 1.

Critical Pitfalls to Avoid

• Do not rely solely on sonographic Murphy sign for diagnosing acute cholecystitis due to low specificity 1
• Do not assume dilated common bile duct equals choledocholithiasis, especially in elderly patients where physiologic dilation occurs 1
• Do not use CT as first-line imaging for suspected gallstones—it misses 25% of stones 2
• Optimize ultrasound technique by adjusting gain, frequency, and focal zone settings to identify small stones and differentiate their shadows from bowel gas 2
• Recognize that gallstones may be mobile—reposition the patient during ultrasound to confirm stone movement 2