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This guideline provides recommendations for the interpretation and evaluation of abnormal liver test results in adults. It should be used in conjunction with other guidelines, such as Clinical Management of Chronic Hepatitis B, Clinical Management of Chronic Hepatitis C, Investigation and Management of Iron Overload and Viral Hepatitis Testing.
Background
Abnormal liver tests may indicate an abnormality of the liver and provide clues as to the nature of the problem. However, in an asymptomatic patient, mild abnormalities may not be clinically significant. A systematic approach to evaluating the patient and ordering further tests will help to efficiently identify any underlying disease.7
Further testing and referrals may not be necessary in many circumstances.
The term ‘liver function test’ should not be used when referring to serum enzyme levels because they correlate poorly with metabolic activities of the liver.
There are two broad categories of liver enzyme abnormalities.7,9 (see Table 2) Usually the most marked abnormality points to the underlying category of disorder.
1. Hepatocellular injury (e.g. hepatitis) – damaged liver cells develop leaky membranes, allowing for escape of intracellular enzymes into the bloodstream.1,3,10 The major intracellular enzymes are aspartate aminotransferase (AST) and alanine aminotransferase (ALT).
2. Cholestasis (e.g. biliary obstruction or hepatic infiltration) – obstructed/damaged intra- or extrahepatic bile ducts cause the induction of synthesis of alkaline phosphatase (ALP) and gammaglutamyl transpeptidase (GGT). In acute biliary obstruction, elevation of these enzyme levels often lags symptoms by approximately 24 hours. An isolated elevation of GGT is a relatively common finding and does not necessarily indicate significant liver disease.7
NOTE: Bilirubin is not a useful test for distinguishing between cholestasis and hepatocellular injury
because it may be elevated in both situations.1,3
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