Blood Investigations for Gallstone Disease
For patients suspected of having gallstones, liver biochemical tests (including ALT, AST, bilirubin, ALP, GGT) and abdominal ultrasound should be performed as the initial diagnostic investigations. 1
Initial Diagnostic Workup
Trans-abdominal ultrasound scanning (USS) and liver function tests (LFTs) are the recommended first-line investigations for patients with suspected gallstones. Normal results do not preclude further investigation if clinical suspicion remains high. 1
A complete liver biochemistry panel should include:
- Bilirubin (total and direct)
- Alkaline phosphatase (ALP)
- Gamma-glutamyl transferase (GGT)
- Alanine aminotransferase (ALT)
- Aspartate aminotransferase (AST) 1
Full blood count (FBC) and international normalized ratio/prothrombin time (INR/PT) should be performed, especially if endoscopic or surgical intervention is being considered. 1
Diagnostic Value and Limitations
The normal liver biochemical tests have a high negative predictive value of 97% for common bile duct stones, but the positive predictive value of any abnormal liver biochemical test result is only 15%. 1
Direct visualization of common bile duct stones on abdominal ultrasound is a very strong predictor of choledocholithiasis, but indirect signs such as increased bile duct diameter are not sufficient to identify patients with common bile duct stones. 1
Liver function abnormalities are common in acute cholecystitis but have limited predictive value for common bile duct stones. In one study, 33% of patients with acute cholecystitis had hyperbilirubinemia, but less than 10% of these cases could be attributed to common bile duct stones. 2
ALT elevation is particularly useful for diagnosing gallstone pancreatitis. A ≥3-fold elevation of ALT (≥150 IU/L) in the presence of acute pancreatitis has a positive predictive value of 95% for gallstone-related pancreatitis. 3
Risk Stratification for Common Bile Duct Stones
Common bile duct stone risk should be stratified according to the modified classification from the American Society of Gastrointestinal Endoscopy and the Society of American Gastrointestinal Endoscopic Surgeons: 1
- Very strong predictors: Visualization of common bile duct stone on ultrasound
- Strong predictors: Common bile duct dilation on ultrasound (>6mm with gallbladder in situ), bilirubin level >4 mg/dl
- Moderate predictors: Abnormal liver function tests other than bilirubin, age >55 years, clinical gallstone pancreatitis
Additional Investigations Based on Risk
For patients with moderate risk for choledocholithiasis, additional investigations should be considered: 1
- Magnetic resonance cholangiopancreatography (MRCP)
- Endoscopic ultrasound (EUS)
- Intraoperative cholangiography
- Laparoscopic ultrasound
In patients with gallstone pancreatitis, a combination of ultrasound and biochemical tests provides the best non-invasive method for rapidly detecting gallstones as an etiological factor. 4
Special Considerations
In patients with suspected gallstone-related pancreatitis, additional blood tests should include serum amylase or lipase, triglyceride level, and calcium level. 1
For patients undergoing biliary sphincterotomy for ductal stones, full blood count and coagulation studies (INR/PT) must be performed prior to the procedure. 1
For patients on anticoagulants or antiplatelet therapy, management should follow established guidelines for patients undergoing endoscopic procedures. 1
Clinical Pitfalls
Normal liver function tests do not exclude the presence of gallstones or even common bile duct stones. If clinical suspicion remains high, further investigations should be pursued. 1
Common bile duct diameter alone is not a reliable predictor of stones, especially in elderly patients where loss of musculature tone may increase the diameter even without stones. 1
Relying solely on biochemical markers without imaging can lead to missed diagnoses, as the positive predictive value of liver function tests for common bile duct stones is limited. 1