Gamma-glutamyl transferase (GGT) as a lab test !

GGT is very sensitive to cholestasis and alcohol but not specific; its main use is confirming that a high ALP is from the liver.

Updated 2026-11-01

Key facts

A membrane enzyme that transfers the γ-glutamyl group of glutathione; it takes part in glutathione recycling.
It is found in liver, bile ducts, kidney and pancreas, but not in bone: so it separates hepatic from bone ALP.
It is induced by alcohol and by enzyme-inducing drugs (phenytoin, carbamazepine, barbiturates).
It is very sensitive but not specific: it rises in fatty liver, obesity, diabetes and heart failure.
Its reference range varies by laboratory and sex.

What it measures: the activity of γ-glutamyl transferase, which cleaves extracellular glutathione so its amino acids can re-enter cells.
Where it comes from: mainly bile canaliculi and ducts; also the proximal renal tubule (but renal GGT goes into urine, not blood).
Why it rises: cholestasis of any cause, alcohol use, inducing drugs, fatty liver, hepatitis, liver metastases.
Pitfalls: an isolated mild GGT rise with nothing else is common and rarely means serious disease; an alcohol-related rise takes weeks to settle after abstinence.
It has been studied as a marker of cardiometabolic risk and oxidative stress, not as a diagnostic test for those diseases.

High ALP with normal GGT points to bone, pregnancy or growth.
In progressive familial intrahepatic cholestasis types 1 and 2, GGT is normal despite cholestasis: a useful exception.
It is used, with MCV and other markers, to follow alcohol abstinence.

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What is GGT mainly used for in practice?

To confirm that a high alkaline phosphatase comes from the liver and not bone, because bone has no GGT.

Which substances induce GGT?

Alcohol and enzyme-inducing drugs such as phenytoin, carbamazepine and barbiturates.

Why is GGT not specific?

It rises in many settings: fatty liver, obesity, diabetes, heart failure, alcohol and drugs, as well as cholestasis.

Which molecule is GGT's natural substrate?

Glutathione: GGT removes its γ-glutamyl group so its amino acids can be recycled.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: Gamma-glutamyl Transferase (GGT) Test: MedlinePlus Medical Test (MedlinePlus, US National Library of Medicine, 2026); Gamma-glutamyl transferase (GGT) blood test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Representative model, for educational purposes only.