Gamma-Glutamyltransferase 

Updated: Dec 11, 2013
  • Author: Rugheed Ghadban, MD; Chief Editor: Eric B Staros, MD  more...
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Reference Range

Gamma glutamyl transferase (GGT) is an enzyme found in cell membranes of many tissues mainly in the liver, kidney, and pancreas. [1] It is also found in other tissues including intestine, spleen, heart, brain, and seminal vesicles. The highest concentration is in the kidney, but the liver is considered the source of normal enzyme activity. [1]

The reference range for gamma glutamyl transferase (GGT) is 0-30 IU/L. In most studies, males and females have equal levels, [2, 3] although some studies have shown elevated GGT in males compared with females, [4] usually 25% higher.

Infants have 6-7 times the upper limit of the adult reference range, which declines to adult levels around age 7 months. [5]

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Interpretation

Gamma glutamyl transferase is found in many different tissues, including the proximal renal tube, liver, pancreas, intestine, spleen, heart, brain, and seminal vesicles.

GGT levels are within the reference range in bone disorders, pregnancy, and muscle disease. GGT levels are usually normal in myocardial infarction (MI); however, they can increase approximately 4 days after MI. [1]

Increased GGT levels are associated with the conditions listed below. [1]

GGT levels are increased in patients withliver diseases in general, including the following: [6]

  • Hepatitis (acute and chronic)
  • Liver metastasis and carcinoma
  • Alcoholic liver disease
  • Primary biliary cirrhosis and sclerosing cholangitis

Extrahepatic causes for GGT level elevation include the following:

  • Pancreatitis
  • Carcinoma of prostate
  • Carcinoma of breast and lung
  • Systemic lupus erythematosus
  • Alcoholism
  • Congestive heart failure and chronic coronary artery disease: The level of elevation correlates with the risk of death secondary to cardiovascular disease. [7]
  • GGT levels may be increased due to medications, such as carbamazepine, cimetidine, furosemide, heparin, isotretinoin, methotrexate, oral contraceptives, phenobarbital, phenytoin, and valproic acid. [8]
  • Smoking may cause elevated GGT levels. [8]
  • GGT levels are higher among blacks.
  • GGT levels may be increased in mononucleosislike syndrome (MLS). [6]
  • Decreased GGT levels are associated with hypothyroidism [1] and early pregnancy. [8]
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Collection and Panels

Pretest considerations include the following:

  • Patient should fast 8 hours before test (except for water). [6]
  • Some authors recommend alcohol abstinence 24 hours before testing, [6] although most references indicates that GGT level may take as long as one month to normalize after abstinence. [9]

Test elements are as follows:

  • Sample - Blood (5mL) [1]
  • Method of collection - Venipuncture
  • Tube - Red topped, red/gray topped, or green topped [6]

Posttest considerations include the following:

  • Avoid sample hemolysis. [6]
  • The sample is stable for as long as 7 days in refrigerator and for months when frozen. [8]
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Background

Description

Gamma glutamyl transferase (GGT) is an enzyme found in cell membranes of many tissues mainly in the liver, kidney, and pancreas. [1] It is also found in other tissues including intestine, spleen, heart, brain, and seminal vesicles. The highest concentration is in the kidney, but the liver is considered the source of normal enzyme activity. [1]

The enzyme catalyzes the transfer of the gamma-glutamyl group from gamma-glutamyl peptides, such as glutathione to an acceptor such as peptides and L-amino acids. Thus, GGT is involved in the transfer of amino acids across the cellular membrane [6] and leukotriene metabolism. [5]

GGT also has an intracellular antioxidant effect because it is involved in gluthathione metabolism, resulting in the formation of cystein, a thiol compound that exerts antioxidant effects. [10] GGT is cleared from the plasma by liver uptake.

GGT has a half-life of 10 days; however, in recovery from alcohol abuse, the half-life may be as long as 28 days. [9]

Indications/Applications

The major clinical value of serum GGT is in evaluating patients with isolated elevation in alkaline phosphatase because differentiating between hepatobiliary and bone causes in these cases can be difficult. Elevated GGT levels support the hepatobiliary source, whereas GGT levels in the reference range strongly argues against that.

GGT levels can also be used to monitor the cessation of alcohol consumption in patients with chronic alcoholism. [1] GGT levels usually take as long as 1 month to normalize after cessation of alcohol consumption.

Considerations

As mentioned above, the major clinical use of GGT is to differentiate between the hepatobiliary and the bone origin of an isolated elevation in alkaline phosphatase. However, other causes for GGT elevation are noted, such as alcohol consumption or the use of certain medications. This makes the use of GGT levels to know the source of elevated alkaline less useful and indicates the use of other tests such as 5′-nucleotidase in these circumstances.

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