This section will review several typical patterns of laboratory values found in liver disease, with their differential diagnosis:

1. An AST value greater than 20 times the upper reference limit.

If the AST increase is due to liver disease rather than heart or skeletal muscle injury, this suggests acute hepatitis virus hepatitis. Less common etiologies are severe liver passive congestion, active cirrhosis, drug-related liver injury (e.g., acetaminophen), and occasionally atypical early extrahepatic bile duct obstruction. If the ALT level is considerably less elevated than the AST level, this suggests the cause is not hepatitis virus hepatitis. A considerably elevated GGT also would be unusual for hepatitis virus hepatitis A or B and would raise the question of alcohol-related active cirrhosis or early common bile duct obstruction.

2. An ALP value elevated more than 4 times the upper limit; AST value elevated less than 10 times the upper limit.

If the ALP is derived from liver rather than bone, this suggests extrahepatic biliary tract obstruction. Serum bilirubin level would be expected to be more than 5 mg/100 ml. Other possible causes are cholestatic drug jaundice, liver space-occupying lesions, primary biliary cirrhosis or primary sclerosing cholangitis, and occasional cases of intrahepatic obstruction of various etiologies.

3. An ALP value elevated less than 3 times the upper limit; AST value elevated less than 10 times the upper limit.

This pattern is the most common one seen in patients with liver disease and can be associated with a wide variety of etiologies, including subsiding hepatitis virus hepatitis, chronic hepatitis, infectious mononucleosis, active cirrhosis, alcohol or drug-induced liver injury or dysfunction, acute cholecystitis, acute pancreatitis, severe fatty liver, primary biliary cirrhosis, sepsis, and liver space-occupying lesions. If the AST or ALT level is significantly elevated longer than 6 months, chronic hepatitis virus hepatitis and certain other conditions (see the box) would have to be considered.

4. An ALP value elevated; AST value not elevated.

If the ALP elevation is due to liver rather than bone and if other nonhepatic causes (such as phenytoin therapy) for the elevated ALP value can be eliminated, this suggests a space-occupying lesion or lesions in the liver. Other possibilities are primary biliary cirrhosis and resolving phase of previous active liver disease.