Biomarker 101: Gamma-glutamyl transferase (GGT)

GGT is one of the more sensitive liver markers, and one of the easiest to move.

What GGT is

Gamma-glutamyl transferase is an enzyme concentrated in the liver, where it helps process drugs and toxins and plays a role in bile handling. When liver cells are damaged or bile flow is obstructed, GGT leaks into the blood.

It is sensitive but not specific — it picks up a wide range of liver-related issues without indicating which. That makes it most useful read alongside ALT and ALP rather than alone.

Why it's measured

GGT is part of a standard liver panel. It has a particular use in combination with ALP: raised together points toward the liver or bile ducts, while a raised ALP with a normal GGT points toward bone instead. That single comparison saves a good deal of unnecessary investigation.

GGT also responds to alcohol, which is why it appears in discussions of alcohol-related liver stress.

What the numbers mean

Reference ranges vary by laboratory and by sex, with men's ranges typically higher. Australian and New Zealand laboratories report GGT in U/L. Read your result against your own report.

What moves GGT

Alcohol raises GGT, and it is sensitive enough that even moderate intake can lift it. Levels generally fall again after a period without drinking, which is one reason repeat testing is useful.

Fatty liver related to excess body fat is a common cause.

Bile duct obstruction — from gallstones or other causes — raises GGT, often markedly.

Liver inflammation or scarring from any cause will raise it.

Medications of many kinds can raise GGT, generally returning to normal once the medication is stopped. That is a decision for the prescribing doctor, never something to act on independently.

Heart failure can also raise GGT through liver congestion.

What GGT won't tell you

• It doesn't identify the cause. GGT is sensitive and non-specific — it says something is affecting the liver, not what.
• It doesn't measure how much you drink. Plenty of people who drink little have raised GGT, and plenty who drink heavily do not.
• A normal result isn't a guarantee. It lowers the likelihood of liver disease without excluding it.
• Higher isn't proportionally worse. The degree of elevation is a rough guide, not a measure of damage.

The bottom line

GGT picks up liver stress early and says little about its origin. Its greatest practical value is alongside ALP, where the two together separate liver causes from bone ones.