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What is being tested?

GGT is an enzyme found mainly in the liver and is normally present in low levels in the blood. When the liver is injured or the flow of bile is obstructed, the GGT level rises. It is therefore a useful marker for detecting bile duct problems.

How is it used?

The GGT test helps to detect liver disease and bile duct injury. Doctors can also use the test to help find out the reason for a raised level of alkaline phosphatase (ALP). Both ALP and GGT are elevated in disease of the bile ducts and in some liver diseases, but only ALP will be elevated in bone disease. If the GGT level is normal in a person with a high ALP, the cause is most likely to be bone disease. GGT can also be used to screen for alcohol abuse (it will be elevated in about 75% of long-term heavy drinkers).

When is it requested?

A doctor usually requests GGT along with other tests to evaluate a person who has signs or symptoms that suggest liver or bile duct disease. Some of the symptoms of liver injury include jaundice, nausea, vomiting, abdominal (around the stomach area) swelling, abdominal pain, pruritus (severe itching), and tiredness.

GGT is increased in most diseases that cause damage to the liver or bile ducts, but is usually not helpful in distinguishing between different causes of liver damage. GGT is also useful in determining the cause of a high ALP. In people with a history of alcohol abuse who are undergoing treatment, GGT may be used to check that the person is following the treatment program.

What does the result mean?

Your doctor is not usually concerned with low or normal levels, but they do tell him/her that it is unlikely that you have liver disease.

Raised GGT levels indicate that something is going on with your liver but not specifically what. In general, the higher the level the greater the damage to your liver. Elevated levels may be due to liver disease, but they may also be due to congestive heart failure, drinking alcohol, and use of many prescription and non-prescription drugs including nonsteroidal anti-inflammatory drugs (NSAIDs), lipid-lowering drugs, antibiotics, histamine blockers (used to treat excess stomach acid production), antifungal agents, anticonvulsants (seizure control medications), antidepressants, and hormones such as testosterone. Oral contraceptives (birth control pills) and clofibrate can decrease GGT levels.

Male       5 – 50 U/L
Female   5 – 35 U/L

The reference intervals shown above are known as a harmonised reference interval. This means that eventually all laboratories in Australia will eventually use this same interval so wherever your sample is tested, the reference interval should be the one shown above. Laboratories are in the process of adopting these harmonised intervals so it is possible that the intervals shown on the report of your results for this test may be slightly different until this change is fully adopted. 

Is there anything else I should know?

Even small amounts of alcohol within 24 hours of your GGT test may cause a temporary increase in the GGT. If this occurs, your doctor may want to repeat the test to verify that it is normal.

Smoking can also increase GGT.

GGT levels fall after meals, so it is best to be tested when you have not eaten for at least 8 hours.

GGT is higher in persons of African ancestry than those of European ancestry.

Several drugs increase (induce) the concentration of GGT in the blood. The increases do not indicate damage to the liver and can be considered an interference.

Common questions

Can my GGT be raised if I don't have any symptoms?

Yes, GGT is very sensitive and can be increased when you don't have symptoms. This elevation may be temporary, perhaps due to medications you are taking or alcohol ingested within 24 hours of the test. If other liver enzymes are normal, your doctor may just wait and then repeat the GGT test. If the GGT is very high and/or your other liver enzymes are raised, your doctor may want to do more extensive testing to search for the cause.

  • I am an alcoholic but I have stopped drinking. Will my GGT ever go back to normal?

Over time, your GGT level will fall from whatever level it was at the time when you stopped drinking alcohol, to a near normal state. It takes at least a month for GGT to return to normal after you stop drinking. Abstaining from alcohol will decrease your chances of further damaging your liver and should allow your liver functions to improve with time.

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