How do you determine the cause of a biliary obstruction from a patient's liver function test panel? In this video, from our Liver Lab Essentials course, we answer this question while exploring the cholesteric pattern of liver function test abnormalities. We'll discuss which enzymes you need to take seriously and outline what you should do if the results aren't clear.
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Interpreting the results of a liver function test can sometimes stump even the most experienced clinicians! In this course, we'll cover which tests to order, the clinical implications of lab abnormalities seen with common liver function tests, and what to do about them. After taking this course, your ability to confidently interpret liver function tests and take the next steps will become second nature!
The cholestatic pattern of liver function test abnormalities indicates biliary obstruction, and occurs when there is a disproportionate elevation in alkaline phosphatase, when compared to ALT and AST. Serum bilirubin may be elevated, and tests for synthetic function, such as prothrombin time, and albumin may be abnormal.
Biliary obstruction or cholestasis may be due to intrahepatic obstruction, or extrahepatic obstruction. Causes of intrahepatic obstruction include primary sclerosing cholangitis, primary biliary cholangitis, drugs such as steroids or chlorpromazine, toxins, and infiltrative diseases like tuberculosis, sarcoidosis, and lymphoma.
Causes of extrahepatic obstruction include gallstones in the common bile duct, tumors, blocking the bile ducts, pancreatitis and strictures. So how can you determine the possible causes of a biliary obstruction? Biliary obstruction is characterized by elevated levels of alkaline phosphatase, typically three times that of normal.
Remember, there are three sources of alkaline phosphatase, liver, bone and placenta. Whenever the source is the liver, gamma glutamyl transpeptidase levels are also raised. Thus, gamma glutamyl transpeptidase can be tested if there is a doubt as to whether the source of the raised alkaline phosphatase is the liver. Note that antimitochondrial antibody levels are raised in primary biliary cholangitis.
The next best test for determining the cause of biliary obstruction in individuals with significantly elevated levels of alkaline phosphatase is imaging, usually ultrasonography of the abdomen. Gallstones in the common bile duct, as well as pancreatic lesions are easily diagnosed on ultrasound.
Further testing by magnetic resonance cholangiopancreatography, MRCP, or endoscopic retrograde cholangiopancreatography, ERCP, may be required to diagnose the different causes of intrahepatic cholestasis. Lastly, liver biopsy may be required if the cause remains undetermined.