GGT (Gamma-Glutamyl Transferase)

Also written as: GGT, gamma GT, GGTP

A liver and bile duct enzyme, often used to clarify where a raised alkaline phosphatase is coming from.

What it measures

The activity of gamma-glutamyl transferase, an enzyme concentrated in the liver and the bile ducts. It leaks into the blood when these tissues are irritated, and its production is easily switched on by alcohol and many medications.

Why a doctor orders it

Its most common use is to clarify an abnormal alkaline phosphatase result - if GGT is also raised, the liver or bile ducts are the likely source rather than bone. It is also used as a sensitive, though not specific, marker of bile duct irritation and alcohol intake.

What is generally associated with a higher result

Broadly associated with bile duct conditions, fatty change in the liver, regular alcohol intake, and a long list of common medications, because the enzyme is very easily induced. It is sensitive but not specific - a raised value points to the liver region without saying what is happening there.

What is generally associated with a lower result

Low values are generally not pursued.

Everyday things that move this number

Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:

Alcohol intake in the days to weeks before the draw
Many common medications, including some anticonvulsants and antibiotics
Body weight, since it tends to run higher with higher weight
Smoking

Questions to take to your appointment

Was this ordered to clarify an alkaline phosphatase result, and what does the pair suggest together?
Could one of my regular medications be raising it?
How long does alcohol influence this value before a blood draw?

Build a printable questionnaire with your own results →

Where to read more

MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .

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