GGT (Gamma-Glutamyl Transferase)

What is GGT (gamma-glutamyl transferase)?

Gamma-glutamyl transferase, GGT for short, is an enzyme found mostly in the liver and bile ducts. It is also present in the kidneys, pancreas and intestine; it takes part in processing glutathione, one of the body's important antioxidants, and in transporting certain substances across cell membranes. In healthy people, only small amounts are present in the blood. When liver cells or the bile ducts are affected, the blood GGT level rises.

GGT is a highly sensitive test for problems in the liver and bile ducts, but on its own it does not identify the cause of a rise. Because alcohol and some medications can increase GGT production in the liver, it is also sensitive to these factors. In the laboratory, GGT activity in serum is measured on automated analyzers and reported in U/L. Since it does not rise in bone diseases, it provides distinguishing information when assessed together with ALP.

When is a GGT test ordered?

GGT is usually ordered together with liver tests such as ALT, AST, ALP and bilirubin. In particular, when ALP is high, it helps determine whether the elevation comes from the liver and bile ducts or from bone. Because it can rise even before liver involvement causes symptoms, it can serve as an early warning.

It can also be used to monitor the effect of alcohol use on the liver or to follow the process of giving up alcohol. It may be part of routine checks for people with conditions that can affect the liver, such as fatty liver, diabetes or excess weight.

• Jaundice, itching, dark urine or pain in the upper right abdomen
• Suspected fatty liver, hepatitis or bile duct disease
• Clarifying whether a high ALP value comes from the liver
• Assessing and monitoring heavy alcohol use
• Long-term treatment with medications that can affect the liver

How do you prepare for a GGT test?

An 8-hour fast is usually recommended for GGT; you may drink only water during this time. Because even a small amount of alcohol can affect GGT, you should not drink alcohol for at least 24 hours before the test. The effect of regular drinking can last for weeks, so sharing your drinking habits openly with your doctor makes interpretation easier. Smoking can also raise the value slightly.

Epilepsy medications, some sedatives and certain other medications can increase GGT production in the liver. Be sure to mention any new medication you have started recently. Tell your doctor about all the products you use, including herbal teas and supplements; do not stop your prescribed medications unless your doctor tells you to. The blood sample is taken from a vein in the arm and the procedure takes a few minutes; if you wish, our nurse can take your sample at your home or workplace.

What does a GGT result mean?

High GGT suggests there may be a problem in the liver or bile ducts. Alcohol use, fatty liver, hepatitis, bile duct obstruction and certain medications are among the most common causes; in bile duct obstruction, GGT usually rises markedly together with ALP. When both enzymes are high, this supports the liver and bile ducts as the source of the problem, whereas a normal GGT with a high ALP points more toward a bone source.

A mild rise in GGT can also be seen in conditions such as obesity, diabetes, pancreatic diseases and heart failure. When an elevation is found, your doctor may order further tests, such as an abdominal ultrasound, to understand the cause; low GGT values usually have no clinical significance. Reference ranges vary by laboratory, age and sex; values are generally higher in men, and this page shows the range of the laboratory that performs the analysis. Your GGT result should be interpreted by your doctor, taking into account your complaints and your other liver tests.