What is Gamma Glutamyl Transferase (GGT)?
Gamma-glutamyl transferase (GGT) is an enzyme found in a number of sites across the body, including the cells of the heart, brain, kidney, liver, spleen and pancreas, with one of its key roles being defending cells from oxidative damage. It is, however, more commonly found in liver cells (hepatocytes), the biliary duct and the gallbladder; collectively known as the biliary system; and its elevation typically indicates injury to the liver or the biliary system.
When GGT levels in the blood are found to be much higher proportionally to ALT and AST (transaminase enzymes) which are found in hepatocytes, it suggests the issue lies within the biliary system. The main function of the biliary system is the production, storage and secretion of bile, a liquid that aids in the digestion of fats in the small intestine. If there is an obstruction of the bile entering the small intestine, cells in the biliary system become damaged, releasing GGT. This typically is seen with gallstones. ALP (alkaline phosphatase), which is also found in the biliary system, would also be elevated in a similar fashion. An elevated ALP however, should never be interpreted in isolation, as it can be elevated in both liver and bone injury, and GGT in conjunction with ALP allows the source of a rise to be distinguished.
When a blood test for GGT is done, it should be done with other liver function tests, so to better establish the cause for elevation.
Why is this analysis important?
To assess for liver disease
To assess for obstruction or disease within the biliary system
Detect liver injury from excess alcohol consumption - GGT in combination with MCV (mean corpuscular volume) has a 95% sensitivity for alcohol abuse
Helps differentiate between liver and bone disease when alkaline phosphatase (ALP) is elevated
Chronic heart failure
The normal GGT values change depending on the laboratory. The doctor will always evaluate the results based on several factors.
GGT levels can be elevated in the following:
Biliary duct obstruction e.g. gallstonesInfection of the gallbladder - cholecystitis (this typically occurs following an obstruction within the biliary system)
In acute or chronic liver disease (which may be caused by hepatitis)
Drug toxicity (e.g. oral contraceptive pills, furosemide)
Chronic kidney disease
Chronic obstructive pulmonary disease
Even the consumption of small amounts of alcohol during the 24 hours before the analysis can temporarily increase GGT levels.
Smokers may also experience increases in GGT levels.
In very early stages of liver disease your liver function tests may be normal - if there is concern regarding any form of liver disease always consult your healthcare professional
Tests that include this marker
Approach to the patient with abnormal liver biochemical and function tests. Lawrence S Friedman, MD. UpToDate Mar 05, 2019
Gamma-glutamyltransferase-friend or foe within?. , Kunutsor SK, . Liver Int. 2016;36(12):1723-1734. doi:10.1111/liv.13221
Gamma glutamyl transferase, Whitfield JB., Crit Rev Clin Lab Sci. 2001;38(4):263-355. doi:10.1080/20014091084227