• Gamma-glutamyl transferase (GGT) is a liver enzyme
• It is usually ordered as part of Liver Function Tests (LFTs) a panel of tests that assesses the health of your liver.
• It is especially useful in diagnosing bile duct disorders.
• Bile is made in your liver then a network of ducts takes it to your gallbladder for storage.
• Liver scarring (fibrosis) can cause the ducts to narrow, restricting the flow of bile. A range of other factors can restrict the flow of bile including alcoholic liver disease, viral hepatitis, metabolic-dysfunction fatty liver disease (MAFLD), gallstones, tumours, inflammation, infections and certain autoimmune diseases.

Gamma-glutamyl transferase (GGT) is an enzyme found mainly in the liver. Normally, you only have low levels in your blood. If your liver is injured or the flow of bile is blocked, the GGT level rises. Measuring the levels of GGT in your blood is a useful test for detecting bile duct problems.

If your doctor suspects you may have liver problems, they will usually order a standard group of blood tests called Liver Function Tests (LFTs) to check the health of your liver. Performed on the same blood sample, they measure several substances made by the liver. GGT is one of these.

Liver Function Tests (LFTs)

LFTs measure enzymes and proteins that are either produced by the liver cells as part of its normal function or released into the blood when liver cells are damaged. Looked at together, along with your symptoms and medical history, they help build a picture of your liver’s health. Either higher or lower than normal levels of these substances can indicate a problem with your liver.

As well as GGT, they measure the enzymes aspartate aminotransferase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP), together with bilirubin (a breakdown product from red blood cells that is removed from the body by the liver) and albumin (the most common protein in your blood which is made by your liver).

Your liver and your bile ducts

The liver makes bile to help digest food and remove waste. Bile is a thick greenish fluid made in the liver cells. Once made, it flows through a network of ducts inside your liver, which transport it to your gallbladder for storage until you need to use it. Your gallbladder sits just underneath your liver.

When food (especially fats) enters the small intestine, the gallbladder releases bile where it helps break down the fats into smaller droplets enabling it to be processed and absorbed by the intestine.

Bile is also important for removing waste and toxins. After your liver cells have broken the waste and toxins down, they pass into the bile ducts to be picked up by bile and transported to the gall bladder, then on to the intestines for removal. For more on this see bilirubin.

Scar tissue causes your liver to shrink and change shape, and this can cause your bile ducts to become blocked.

Bile duct problems: GGT is a particularly useful test in detecting bile duct problems because it tends to rise quickly when bile flow is impaired. Elevated bilirubin, another LFTs test, can also be a sign of bile duct blockage.

Distinguishing liver from bone disease: GGT is increased in most diseases that cause damage to the liver or bile ducts, but it is usually not helpful in distinguishing between different causes of liver damage. However, it can help to find out the reason for high ALP. Both ALP and GGT are high 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.

Heavy alcohol use: GGT will be higher in about 75 percent of long-term heavy drinkers. If you are a heavy drinker and stop, your GGT level will fall to near normal over time. It takes at least one month for GGT to return to normal after you stop drinking.

Sample

Blood.

Any preparation?

None.

Reading your test report

Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

• GGT is very sensitive and can be increased even when you don't have symptoms. The rise may be temporary, perhaps due to medications you are taking or alcohol taken within 24 hours of the test. If other liver enzymes are normal, your doctor may wait and repeat the GGT test. If the GGT is very high and/or your other liver enzymes are raised, they may want to do more extensive testing to search for the cause.
• Even small amounts of alcohol within 24 hours of your GGT test may cause a temporary increase in 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 eight hours.
• Several drugs increase the level of GGT in the blood. These increases do not indicate damage to the liver, and they are considered an interference.
• There are ethnic variations in GGT levels. For instance, GGT is higher in people of African ancestry than those of European ancestry.

Reference intervals
Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people.
• When compared against them your results may be flagged high or low if they sit outside this range.
• Many reference intervals vary between labs so only those that are standardised or harmonised across most laboratories are given on this website.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation. Your results need to be interpreted by your doctor.

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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