Criteria to Detect Choledocholithiasis
All patients with suspected choledocholithiasis should undergo risk stratification using a combination of clinical predictors, liver biochemical tests, and abdominal ultrasound to determine the need for further diagnostic imaging or therapeutic intervention. 1
Initial Screening Tests
Every patient requires the following baseline evaluation:
- Liver biochemical tests: ALT, AST, total bilirubin, alkaline phosphatase (ALP), and GGT 1
- Abdominal ultrasound to assess for:
Important caveat: Normal liver biochemical tests have a 97% negative predictive value, but abnormal tests alone have only a 15% positive predictive value for choledocholithiasis. 1 Similarly, CBD diameter >10mm is associated with only 39% incidence of stones, while diameter <9.9mm still carries 14% risk. 1, 2
Risk Stratification System
High-Risk Criteria (Proceed directly to ERCP)
- Direct visualization of CBD stone on ultrasound (very strong predictor) 1, 2
- Total bilirubin >4 mg/dL with dilated CBD 2
- Clinical cholangitis (fever, jaundice, right upper quadrant pain) 1
Moderate-Risk Criteria (Perform MRCP or EUS before ERCP)
- Dilated CBD on ultrasound (>6mm) 3
- Total bilirubin >2 mg/dL 3
- Alkaline phosphatase >190 IU/L 3
- AST >40 IU/L 3
A scoring system using these four moderate-risk factors shows: 3 or more positive factors = >95% positive predictive value (proceed to endoscopic intervention); 0 factors = 100% negative predictive value (rules out CBD stones). 3 With 1-2 positive factors, further evaluation with MRCP or EUS is recommended. 3
Low-Risk Criteria (No further imaging needed)
- Normal liver biochemical tests 1
- Normal CBD diameter on ultrasound 1
- No clinical signs of biliary obstruction 1
Advanced Imaging When Indicated
MRCP (Magnetic Resonance Cholangiopancreatography)
MRCP is the preferred non-invasive test for moderate-risk patients, with sensitivity of 85-100%, specificity of 90%, and accuracy of 89-90% for detecting choledocholithiasis. 1 In the specific context of acute pancreatitis, MRCP demonstrates 97.98% sensitivity and 84.4% specificity. 1
Performance limitations: Sensitivity decreases to 72.7% when CBD diameter exceeds 10mm (versus 88.9% with normal diameter). 4 MRCP should be used instead of diagnostic ERCP when ultrasound is negative but clinical suspicion remains, particularly in the absence of cholangitis or severely abnormal liver function tests. 1
Endoscopic Ultrasound (EUS)
EUS serves as an accurate alternative to MRCP for screening choledocholithiasis, particularly useful when MRCP is contraindicated or unavailable. 1 EUS can be performed at admission or after recovery and is preferred as the initial test for recurrent unexplained pancreatitis. 1
ERCP (Endoscopic Retrograde Cholangiopancreatography)
ERCP should be reserved for therapeutic intervention, not routine diagnosis, given its invasive nature and complication risk. 1
Urgent ERCP (within 24 hours) is indicated for:
- Gallstone pancreatitis with concomitant cholangitis 1
Early ERCP (within 72 hours) is indicated for:
- Visible CBD stone on non-invasive imaging 1
- Persistently dilated CBD with high clinical suspicion 1
- Persistent jaundice 1
Common Pitfalls to Avoid
- Do not rely on CBD diameter alone: Elderly patients may have physiologic dilatation without stones due to loss of musculature tone. 1
- Do not assume negative ultrasound excludes choledocholithiasis: Ultrasound sensitivity for CBD stones ranges only 22.5-75%, and many stones are not visualized. 2 Small stones, cholesterol stones, and stones in the distal CBD are particularly easy to miss. 2
- Do not perform routine ERCP without risk stratification: In 82% of patients undergoing MRCP first, subsequent invasive testing was required, but this selective approach avoids unnecessary ERCP complications in low-risk patients. 5
- Document technical limitations: Bowel gas, body habitus, and patient tenderness can prevent adequate ultrasound examination and should be noted when present. 2