GGT — Gamma-Glutamyl Transferase

What is GGT?

Gamma-glutamyl transferase (GGT) is an enzyme found in high concentrations in the cells lining the bile ducts, liver, kidneys, and pancreas. Its primary physiological role involves the metabolism of glutathione — the body's main intracellular antioxidant — and the transport of amino acids and peptides across cell membranes.

In clinical medicine, GGT is valued above all as the most sensitive routine blood marker for alcohol-related liver injury. Even moderate-to-heavy regular alcohol consumption — below the threshold that causes obvious symptoms — reliably raises GGT, often before ALT, AST, or bilirubin become abnormal. This makes it an invaluable early warning marker in routine liver health screening.

Beyond alcohol, GGT is raised by bile duct obstruction (cholestasis), non-alcoholic fatty liver disease (NAFLD), enzyme-inducing medications, and any chronic liver condition. When interpreted alongside ALT, ALP, bilirubin, and albumin, it helps clinicians distinguish between hepatocellular injury (liver cell damage) and cholestatic disease (bile duct obstruction). GGT alone is not specific to any single cause — pattern analysis across the full liver panel is essential.

Normal GGT range

GGT reference ranges differ between males and females:

• Men: 10–71 U/L
• Women: 6–42 U/L
• GGT typically rises with age in both sexes
• Even moderate regular alcohol consumption can push GGT above the reference range within 2–4 weeks
• GGT normalises within 4–6 weeks of complete abstinence from alcohol

What a high GGT may indicate

A raised GGT warrants interpretation alongside the full liver panel and clinical context. Common causes include:

• Alcohol use — by far the most common cause in the UK; GGT is the single most sensitive routine marker for regular or excessive drinking, rising after as little as 2–4 weeks of elevated intake
• Non-alcoholic fatty liver disease (NAFLD) — fatty infiltration of the liver driven by obesity, insulin resistance, and metabolic syndrome; increasingly common; often detected only on blood tests or imaging
• Bile duct obstruction (cholestasis) — gallstones, biliary strictures, primary biliary cholangitis (PBC), and primary sclerosing cholangitis (PSC); GGT rises alongside ALP
• Enzyme-inducing medications — anti-epileptic drugs (phenytoin, carbamazepine), rifampicin, and some herbal supplements induce hepatic enzyme activity, raising GGT without causing liver damage
• Chronic liver disease from any cause — viral hepatitis B/C, autoimmune hepatitis, haemochromatosis; GGT is a non-specific but sensitive marker of ongoing hepatic injury

What a low GGT may indicate

A GGT within or below the reference range is entirely normal and not associated with any clinical condition. Low GGT requires no action or investigation:

• A low or normal GGT does not exclude all liver disease — GGT can be normal in very early liver conditions or certain genetic conditions affecting GGT specifically
• In a pattern where ALP is raised but GGT is normal, liver disease is less likely — raised ALP with normal GGT usually points to bone disease rather than a liver source
• Low GGT is not a recognised pathological finding

Get your GGT tested at The Vesey

GGT is included in the following panels at The Vesey Private Hospital, Sutton Coldfield. It is always reported as part of a complete liver enzyme panel:

• Liver Health Panel — GGT, ALT, AST, ALP, bilirubin, albumin, total protein (full liver function assessment)
• Lifestyle Screen — comprehensive multi-system panel including full liver function
• Advanced Health Panels — full metabolic, liver, and organ-function assessment

No fasting strictly required, though ideally fast for 4 hours before a liver panel. Avoid alcohol for at least 48 hours before the test for the most accurate baseline. Results reviewed by a clinician before release.

Frequently asked questions

Further reading: GGT — Lab Tests Online UK · Independent patient information from the British Society for Clinical Biochemistry.