Empeiria

Gamma-glutamyl transferase

Also known as GGT, gamma GT, GGTP

enzyme activity · no single molecular formula

LOINC 2324-2 code verified serum U/L

What this substance is

Reported in U/L, units of catalytic activity. GGT moves the gamma-glutamyl group of glutathione onto other molecules; the test times that transfer.
What it catalyses

EC 2.3.2.2

a (5-L-glutamyl)-peptide + an amino acid = a peptide + a 5-L-glutamyl amino acid

UniProt P19440

The reaction the test times
Glutathione, its main natural substrate

Each molecule is drawn from ChEBI's curated 2D drawing, accepted only after its InChIKey, formula and charge matched the ChEBI release. Atom diagrams are checked against the NIST Atomic Spectra Database.

3D model

Predicted structure of GGT's single precursor chain (AlphaFold). The working enzyme is this chain cut into two parts. Predicted by AlphaFold (model v6, average confidence 95 of 100); its sequence matches UniProt exactly. Colour is AlphaFold's own confidence for each part: dark blue very high (above 90), light blue confident (70-90), yellow low (50-70), orange very low (below 50). Drag to rotate, scroll to zoom.

Reference ranges

Checking your own result against this range needs the running application; this is a static copy. Nothing you type anywhere in Empeiria is ever sent to a server.

This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.

How it is measured

In practice

A health worker takes a small blood sample from a vein in your arm with a needle. Alcohol, smoking and some medicines can change the result. GGT levels drop after meals, so your provider may ask you to fast first.

Venous blood sample by venipuncture. Results may be affected by certain medicines or supplements, alcohol and cigarette smoking; GGT falls after meals, so a period of fasting may be requested.

Before the test

  • Ask your provider for specific instructions; you may be asked to fast for a set time.

Where: laboratory

Source: Gamma-Glutamyl Transferase (GGT) Test, MedlinePlus (U.S. National Library of Medicine) cited · not yet checked by a person

In the lab

kinetic enzyme

Kinetic colorimetric (Szasz, carboxy-nitroanilide substrate)

GGT is a helper protein that cuts a piece off a test chemical. When the piece comes off, the liquid turns yellow. The machine times how fast the colour appears, and a faster change means more GGT.

GGT transfers the gamma-glutamyl group from a gamma-glutamyl-carboxy- nitroanilide substrate to glycylglycine, releasing 5-amino-2-nitrobenzoate; the rate of colour formation at 415 nm is proportional to GGT activity (a modification of the Szasz method).

  • Read by: Rate of absorbance increase at 415 nm (secondary 700 nm)

What can throw it off

  • IgM gammopathy (rare)
Why labs disagree: GGT results fall into distinct method groups. In an eight-platform comparison on serum from healthy volunteers, GGT was rated "red" (bias probably prevents one shared reference interval) and showed up to four discrete method groups, with one analyser family reading 18-20% below the average. All the methods were modifications of the IFCC-recommended method, but measuring the activity of the same enzyme under different conditions can give different results.

Sources: Koerbin G et al. Bias Assessment of General Chemistry Analytes using Commutable Samples. Clin Biochem Rev 2014;35:203-211 (PMC4310060); NHANES 2017-2018 Laboratory Procedure Manual, Gamma-Glutamyltransferase (GGT), CDC/NCHS cited · not yet checked by a person

What it reports on

Associated symptoms

Conditions this marker features in

When high
  • high Blocked or slowed bile flow · defining
    GGT is part of the same cut-off (above 3 times the upper limit of normal), and a raised GGT confirms that a raised ALP comes from the liver rather than bone. Some rare inherited forms of cholestasis have a normal GGT.
  • high Fatty liver · supportive
    GGT may be 2-3 times the upper limit in more than half of patients.
  • high Liver damage from alcohol · supportive
    Often raised and helps support the diagnosis, but it is not specific to alcohol.

Ordered as part of

hepatic