Recognizing a cholestatic pattern on a liver function panel

Three abnormal patterns can be recognized when interpreting the results of a liver testing panel. These include the hepatocellular pattern, the cholestatic pattern, and the isolated hyperbilirubinemia pattern. Now, let’s focus on the 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.

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.

There are four additional tests to consider when determining the cause of biliary obstruction:

1. Further serum testing
2. Ultrasound
3. Magnetic resonance imaging (MRI) or x-ray
4. Biopsy

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.

Ultrasound

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.

Biopsy

Lastly, a liver biopsy may be required if the cause of the biliary obstruction remains undetermined.

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