From the Guidelines
The most reliable initial lab value to order alongside Magnetic Resonance Cholangiopancreatography (MRCP) to rule out choledocholithiasis is gamma-glutamyl transpeptidase (GGT), with a sensitivity of 80.6% and a specificity of 75.3%, using a cut-off level of 224 IU/L, as it has been shown to be the most reliable liver function test (LFT) in this context 1. When evaluating patients for choledocholithiasis, it is essential to consider the role of laboratory tests in conjunction with MRCP. The study by 1 highlights the importance of LFTs, particularly GGT, in diagnosing common bile duct stones.
- Key lab values to consider include:
- GGT: with a cut-off level of 224 IU/L, it has a sensitivity of 80.6% and a specificity of 75.3% for diagnosing choledocholithiasis 1
- Other LFTs, such as total bilirubin, direct bilirubin, alkaline phosphatase (ALP), aspartate aminotransferase (AST), and alanine aminotransferase (ALT), may also be useful in establishing the likelihood of biliary obstruction and guiding interpretation of MRCP findings
- Complete blood count (CBC) with white blood cell count and lipase/amylase levels can help identify inflammatory responses and rule out concurrent pancreatitis The combination of these lab values, particularly GGT, with MRCP imaging provides a comprehensive assessment for accurate diagnosis of common bile duct stones, allowing for appropriate treatment planning. It is crucial to note that the diagnosis of choledocholithiasis is often confirmed with endoscopic retrograde cholangio-pancreatography (ERCP), and the results of laboratory tests should be interpreted in the context of clinical presentation and imaging findings 1.
From the Research
Initial Lab Values to Order Alongside MRCP
To rule out choledocholithiasis, the following lab values can be considered alongside Magnetic Resonance Cholangiopancreatography (MRCP):
- Total bilirubin
- Alkaline phosphatase (ALP)
- Aspartate aminotransferase (AST)
- Alanine aminotransferase (ALT)
- Amylase
Rationale for Lab Value Selection
The selection of these lab values is based on studies that have investigated the diagnostic accuracy of various tests for choledocholithiasis. For example, a study published in the Indian Journal of Gastroenterology found that dilated bile duct on ultrasonography, raised total bilirubin, raised ALP, raised amylase, raised SGPT, and SGOT were significantly associated with choledocholithiasis 2. Another study published in the Journal of Clinical Gastroenterology found that patients with choledocholithiasis may have elevated liver tests, including AST and ALT, although this is not a common occurrence 3.
Predictive Value of Lab Values
A scoring system consisting of four factors, including dilated bile duct on ultrasonography, total bilirubin >2 mg/dL, ALP >190 IU/L, and SGOT >40 IU/L, has been proposed to predict the risk of choledocholithiasis 2. A positive predictive value of 3 or more factors was over 95%, necessitating an endoscopic intervention. In patients with a negative MRCP, a total bilirubin >3 mg/dL was found to predict a bile duct stone 4.
Utility of MRCP
MRCP has been found to have a high sensitivity and specificity for diagnosing choledocholithiasis, comparable to endoscopic ultrasound (EUS) and ERCP 5, 6. However, the utility of MRCP in clinical decision-making is still a topic of debate, with some studies suggesting that it may not change the management of patients with suspected choledocholithiasis 5.
Considerations for EUS
In patients with intermediate risk of choledocholithiasis and a negative MRCP, EUS can be considered if clinical suspicion is still present, especially if the total bilirubin is above 3 mg/dL 4. The diagnostic yield of EUS in this setting is around 14% 4.
Summary of Key Findings
- Total bilirubin, ALP, AST, ALT, and amylase are relevant lab values to order alongside MRCP to rule out choledocholithiasis.
- A scoring system consisting of four factors, including dilated bile duct on ultrasonography, total bilirubin >2 mg/dL, ALP >190 IU/L, and SGOT >40 IU/L, can predict the risk of choledocholithiasis.
- MRCP has a high sensitivity and specificity for diagnosing choledocholithiasis, but its utility in clinical decision-making is still debated.
- EUS can be considered in patients with intermediate risk of choledocholithiasis and a negative MRCP if clinical suspicion is still present.