Liver enzymes and the liver function panel

In this article, learn how to decipher common liver enzyme test panels for liver function and disease.
Last update26th Jan 2021

Several liver enzymes are commonly measured in blood serum, and each one has a normal range in healthy patients.

Table 1. Liver enzymes that are commonly measured in blood serum, and their normal ranges.

Now, let’s take a look at what we can learn from each of these liver enzymes.

What can serum alanine aminotransferase and aspartate aminotransferase testing tell us?

The breakdown of hepatocytes results in the release of aminotransferases such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST) into the blood. Therefore, elevated levels of these enzymes indicate liver injury.

Alanine aminotransferase is a cytosolic enzyme only found in hepatocytes and is specific to liver disease. Aspartate aminotransferase is a mitochondrial enzyme in the liver, but it is also found in the heart, muscle, kidney, and brain. So, AST is nonspecific to liver disease.

Figure 1. Elevated serum alanine aminotransferase (ALT) levels are specific to liver disease, whereas elevated aspartate aminotransferase (AST) levels are nonspecific to liver disease.

What can serum alkaline phosphatase testing tell us?

Alkaline phosphatase (ALP) is present in the liver, bone, intestine, and placenta. Production of ALP is increased during cholestasis, which is a decrease in bile flow due to intrahepatic or extrahepatic causes.

It is important to determine if the source of ALP is the liver or another organ. If gamma-glutamyl transpeptidase (GGT) or 5’-nucleotidase levels are increased alongside ALP, we can assume that the source of the ALP is the liver.

Figure 2. Elevated levels of gamma-glutamyl transpeptidase (GGT), alkaline phosphatase (ALP), and 5’-nucleotidase indicate cholestasis that is caused by the liver.

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What can serum GGT testing tell us?

Gamma-glutamyl transpeptidase is a microsomal enzyme produced by the biliary epithelium. Gamma-glutamyl transpeptidase is elevated in the liver, biliary tract, and pancreas diseases as well as common bile duct obstruction. When seen in conjunction with the transaminases (e.g., ALT and AST), GGT is also a marker of alcohol abuse.

Figure 3. Elevated gamma-glutamyl transpeptidase (GGT) may indicate a disease of the liver, biliary tract, pancreas, or a common bile duct obstruction. Elevated serum levels of GGT, alkaline phosphatase (ALP), and aspartate aminotransferase (AST) may indicate alcohol abuse.

What can serum 5’-nucleotidase testing tell us?

The serum 5'-nucleotidase enzyme is derived from the plasma membranes of liver cells. It is elevated in hepatobiliary diseases.

In cholestatic conditions, ALP, GGT, and 5’-nucleotidase levels are all elevated.

Figure 4. The enzyme 5’-nucleotidase is elevated with hepatobiliary diseases.

So, there you have it! Elevated liver enzymes, whether alone or in combination, can provide information that helps clarify the clinical picture of your patient.

Table 2. Summary of conditions associated with elevated levels of the liver enzymes alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), gamma-glutamyl transpeptidase (GGT), and 5'-nucleotidase.

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Recommended reading

  • Chalasani, N, Younossi, Z, Lavine, JE, et al. 2012. The diagnosis and management of non-alcoholic fatty liver disease: practice guideline by the American Gastroenterological Association, American Association for the Study of Liver Diseases, and American College of Gastroenterology. Gastroenterology142: 1592–1609. PMID: 22656328
  • Fuchs, S, Bogomolski-Yahalom, V, Paltiel, O, et al. 1998. Ischemic hepatitis: clinical and laboratory observations of 34 patients. J Clin Gastroenterol26: 183–186. PMID: 9600366
  • Lok, ASF and McMahon, BJ. 2007. Chronic hepatitis B. Hepatology45: 507–539. PMID: 17256718
  • Moussavian, SN, Becker, RC, Piepmeyer, JL, et al. 1985. Serum gamma-glutamyl transpeptidase and chronic alcoholism. Influence of alcohol ingestion and liver disease. Dig Dis Sci30: 211–214. PMID: 2857631
  • Myers, RP, Cerini, R, Sayegh, R, et al. 2003. Cardiac hepatopathy: clinical, hemodynamic, and histologic characteristics and correlations. Hepatology37: 393–400. PMID: 12540790
  • Rej, R. 1978. Aspartate aminotransferase activity and isoenzyme proportions in human liver tissues. Clin Chem24: 1971–1979. PMID: 213206
  • van de Steeg, E, Stránecký, V, Hartmannová, H, et al. 2012. Complete OATP1B1 and OATP1B3 deficiency causes human Rotor syndrome by interrupting conjugated bilirubin reuptake into the liver. J Clin Invest122: 519–528. PMID: 22232210

About the author

Amer Wahed, MD FRCPath
Professor and Vice Chair (Clinical Pathology) and Associate Residency Program Director in the Department of Pathology and Laboratory Medicine at the University of Texas, Health Science Center at Houston, USA.
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