Gamma-Glutamyl Transferase (GGT)

If your liver or bile duct is damaged, GGT may leak into your bloodstream. So high levels of GGT in your blood may be a sign of liver disease or damage to the bile ducts. Bile ducts are tubes that carry bile in and out of the liver. Bile is a fluid made by the liver that is important for digestion. GGT tends to rise in nearly all forms of liver disease, and it is especially sensitive at picking up problems that block the flow of bile, such as gallbladder inflammation, bile duct inflammation, or a blocked bile duct. GGT is also useful in monitoring liver damage from heavy alcohol use and in following primary or secondary liver tumors.

A GGT test can't diagnose the specific cause of liver disease. The test can only indicate that your liver is being damaged. This test is usually done with or after other liver function tests, most often an alkaline phosphatase (ALP) test. ALP is another type of liver enzyme. While both your GGT and ALP may be elevated in diseases that affect your bile ducts and liver, only ALP will be elevated in bone disease. Because GGT stays normal when bone is the problem, comparing the two helps your provider tell whether the issue is in your liver and bile ducts or in your bones.

If your results show higher-than-normal GGT, it usually means there's a problem with your liver or with the flow of bile out of the liver.

Very high GGT (often 5 to 30 times the normal level) is most often caused by a blockage in the bile ducts, such as from gallstones, scarring, or a tumor.

Smaller increases (about 2 to 5 times normal) are common with viral hepatitis, fatty liver disease, and chronic alcohol use. GGT is one of the most sensitive lab tests for picking up regular heavy drinking, and is often raised in people with alcohol-related liver disease even before other liver tests change.

Some prescription medicines, including phenytoin and phenobarbital, can also raise GGT without there being any liver damage.

If your results show normal GGT, you probably don't have liver disease, even if your alkaline phosphatase (ALP) is high. A normal GGT alongside a high ALP suggests the problem is in the bones rather than the liver. GGT does not rise in normal pregnancy or in healthy children's growing bones, which makes it a useful tie-breaker.

Because GGT can be high for many reasons, your provider will usually look at it alongside other liver tests and your symptoms before making a diagnosis.