How can I recognize a cholestatic pattern?
The cholestatic pattern of liver function test abnormalities indicates biliary obstruction. The pattern occurs when there is a disproportionate elevation in alkaline phosphatase (ALP) compared to alanine aminotransferase (ALT) and aspartate aminotransferase (AST).
Serum bilirubin can also be elevated. Tests for synthetic function, such as prothrombin time (PT) and albumin, may be abnormal.
What causes biliary obstruction?
Biliary obstruction or cholestasis can be due to intrahepatic or extrahepatic obstruction. Causes of intrahepatic obstruction include primary sclerosing cholangitis, primary biliary cholangitis, drugs (e.g., steroids or chlorpromazine), toxins, and infiltrative diseases (e.g., tuberculosis, sarcoidosis, or lymphoma). On the other hand, causes of extrahepatic obstruction include gallstones in the common bile duct, tumors blocking the bile ducts, pancreatitis, and strictures.
How do you determine the possible cause of a biliary obstruction?
There are four additional tests to consider when determining the cause of biliary obstruction:
- Further serum testing
- Magnetic resonance imaging (MRI) or x-ray
Further serum testing
Biliary obstruction is characterized by elevated levels of ALP, typically three times the normal level. Remember that there are three sources of alkaline phosphatase—the liver, bone, and placenta.
Whenever the source of elevated ALP is the liver, gamma-glutamyl transpeptidase (GGT) levels are also raised. Thus, gamma-glutamyl transpeptidase can be tested if there is a doubt about the source of the elevated ALP.
In addition to elevated ALP, antimitochondrial antibody (AMA) levels are also raised in primary biliary cholangitis.
The next best test for determining the cause of biliary disease in individuals with significantly elevated levels of ALP is imaging such as ultrasonography of the abdomen. Gallstones in the common bile duct and pancreatic lesions are easily diagnosed on ultrasound.
Magnetic resonance imaging or x-ray
Further testing by magnetic resonance cholangiopancreatography or endoscopic retrograde cholangiopancreatography may be required to diagnose differential causes of intrahepatic obstruction.
Lastly, a liver biopsy may be required if the cause of the biliary obstruction remains undetermined.
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