Gamma-Glutamyl Transferase (GGT)
A liver and bile duct enzyme. A higher level can be linked to alcohol, some medicines, fatty liver or bile duct problems.
AI-verified against cited sources. Awaiting expert reviewAlso called GGT, GGTP, γ-GTLOINC 2324-2
Check your result
The usual range for GGT depends on sex. Choose female or male above to see where you stand.
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What it is
Gamma-glutamyl transferase (GGT) is an enzyme found on the surface of cells throughout the body, especially in the liver and bile ducts. It helps recycle glutathione, one of the body's main antioxidants. A small amount reaches the blood, and this test measures how active it is there. It is usually ordered with other liver tests, most often alkaline phosphatase (ALP).
Why it matters
GGT is a sensitive sign that the liver or bile ducts may be under strain. A common use is to help sort out a high ALP: if GGT is high too, the liver or bile ducts are the likely source, and if GGT is in the usual range, bone is more likely. GGT also rises with regular alcohol use, some medicines, extra body weight and fatty liver, so a raised result does not point to one cause. It is read together with your other liver tests, your history and how you feel.
If it’s low
Most labs print a range that starts at or near zero, so a low GGT is rarely flagged. A low result is usually not a concern, and many healthy people have low values.
Common causes
- Everyday differences between people
- An underactive thyroid, which Labcorp lists as a cause of lower GGT
- Lower triglycerides after treatment, which Labcorp notes can bring GGT down
If it’s high
A GGT above your lab's range is a sign that your liver or bile ducts may be under strain, but it does not say why. Mild rises are common and often have everyday explanations, such as alcohol, extra body weight, fatty liver or a medicine. Larger rises, especially with a high ALP, are more often linked to a blocked or irritated bile duct. Many other things can cause this, and your clinician can put the result in context.
Common causes
- Alcohol, including drinking in the day before the test, or regular drinking over time
- Medicines that make the liver more active, such as phenytoin, phenobarbital or warfarin, and many others
- Smoking
- Extra body weight and fatty liver disease
- Diabetes or high triglycerides
- Heart failure
- Viral or other hepatitis, or cirrhosis
- A blocked or inflamed bile duct, for example from gallstones or primary biliary cholangitis
- Pancreatitis
- Infectious mononucleosis or an overactive thyroid
- Less often, tumors of the liver or pancreas
What can help
- Tell your clinician how much alcohol you drink and every medicine and supplement you take
- Ask whether to repeat the test, along with ALT, AST, ALP and bilirubin, after a few weeks
- Healthy-liver habits that clinicians often discuss include limiting alcohol, staying active and aiming for a weight that suits you
- Ask whether a liver ultrasound or other tests would help find the cause
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
The usual range depends on sex. Choose women or men to see the one that applies.
- Men, 18+0–65 U/L
Sources: Labcorp, Clinica Chimica Acta, Gastroenterology, Cleveland Clinic
- Women, 18+0–60 U/L
Sources: Labcorp, Clinica Chimica Acta, Gastroenterology, Cleveland Clinic
See GGT by age and sex, with the U.S. survey numbers where they exist.
If this applies to you
GGT means a little more for some people. Open the one that fits you.
Fatty liver or liver condition
GGT is most often raised by extra weight, alcohol or some medicines, so on its own it isn't specific to liver disease. BSG keeps it in the first liver panel because in fatty liver and alcohol-related liver disease it helps pick up cases that other liver tests can miss.
Tracking for long-term health
GGT is a liver enzyme that alcohol raises. Smoking, some medicines and supplements, and conditions such as diabetes and heart failure can also affect it, so a high GGT on its own doesn't show the cause.
How common is your level?
NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.
Use the left and right arrow keys to read each age. Shift moves five years.
Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.
Explore GGT by age and sex: every percentile as a table, with a download.
What can affect your result
- Sex: results run a little higher in men than in women, and labs print separate ranges
- Alcohol: even small amounts in the day before the test can raise it
- Body weight, blood sugar and triglycerides: all are linked to higher GGT
- Smoking and medicines or supplements, especially enzyme-inducing ones such as phenytoin and phenobarbital
- Eating: levels are lower after meals, so many labs ask for a fast of about 8 hours
- Age: infants differ from adults, and after infancy age has only a small effect on most lab ranges
- Alcohol, even in small amounts, can raise GGT. Cleveland Clinic suggests none for at least 24 hours before the test.
- Smoking and some medicines and supplements can change the result (MedlinePlus).
- Phenytoin and phenobarbital raise GGT. Labcorp calls these false elevations for liver disease and suggests other tests for people who take them.
- Labcorp rejects samples with gross hemolysis or lipemia, and does not accept EDTA, citrate or oxalate plasma.
Labcorp asks for an 8-hour fast, and GGT is lower after meals, so drawing under the same fasting conditions each time makes results easier to compare. Varies with the cause. Your clinician can suggest when a repeat test is likely to show a change after a shift in alcohol use, medicines or body weight.
When to talk to a clinician
No urgent threshold has been published for GGT. See a clinician soon if a result outside your lab's range comes with yellow skin or eyes, severe itching, belly pain or swelling, loss of appetite, or nausea and vomiting. If you feel well, mention the result at your next visit.
Questions you could ask
- How does my GGT fit with my other liver tests?
- How often should I recheck my liver tests?
- Could any of my medicines or supplements explain this result?
- Should we repeat the test along with ALT, AST, ALP and bilirubin?
- Would a liver ultrasound or another test help find the cause?
- How might my alcohol use, weight or blood sugar be affecting this number?
Questions people ask
Can one night of drinking raise my GGT?
Yes. Even small amounts of alcohol can raise GGT, which is why some clinics ask you not to drink for at least 24 hours before the test. Regular drinking can keep it raised over time.
My GGT is high but my other liver tests are in the usual range. Should I worry?
GGT reacts to more things than ALT or AST do, so it can be raised on its own. Alcohol, some medicines, extra body weight, fatty liver and smoking can all do this. One high result is a reason to talk with your clinician, and often to repeat the test. It is not a diagnosis.
What is the difference between a high GGT and a high ALP?
Both can rise when the liver or bile ducts are under strain. ALP also comes from bone, but GGT does not. A high ALP with a high GGT points more toward the liver or bile ducts. A high ALP with a GGT in the usual range makes a source such as bone more likely.
Is a lower GGT better? What is the best level?
Large studies link higher GGT with higher rates of heart disease, diabetes and earlier death. These are links, not proof that GGT causes harm, because GGT often rises together with alcohol use, weight and blood sugar. No guideline sets a target number, so no wellness target is shown here. Your lab's range is the best guide, and your clinician can say what matters for you.
How do I convert between U/L and µkat/L?
Multiply µkat/L by 60 to get U/L, so 0.5 µkat/L is 30 U/L. To go the other way, divide U/L by 60. Most reports use U/L, and some labs use µkat/L.
Show the science and sources
Units
- 1 U/L = 1 U/L
- 1 U/L = 0.01667 µkat/L
Is a change real?
GGT naturally varies about 8.9% from test to test in the same healthy person. Between two results from the same lab, a rise of 41% or more, or a fall of 29% or more, is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: The European Biological Variation Study (EuBIVAS): a summary report.
For clinicians and researchers
GGT (EC 2.3.2.2) is a membrane-bound enzyme that transfers the gamma-glutamyl group from glutathione and other peptides to amino acids, which supports glutathione recycling and defence against oxidative stress. The enzyme is present in the kidney, liver, pancreas and other tissues, but serum activity comes mainly from the liver and bile ducts, and GGT stays in the usual range in most kidney failure. Unlike ALP, it has no bone or placental source, which is why it is used to confirm that a raised ALP is hepatobiliary. Enzyme induction by alcohol and drugs such as phenytoin and phenobarbital raises serum GGT without hepatocyte damage, which makes it sensitive but not specific for hepatobiliary disease. It is a widely used but non-specific marker of alcohol intake and is often paired with carbohydrate-deficient transferrin (CDT) for that purpose. Assays are kinetic enzymatic methods. IFCC reference procedures run at 37 °C, and results from older methods run at lower temperatures are not comparable. Reference limits depend on method and population: an IFCC-procedure study of hospital patients gave preliminary 97.5th percentile limits of 55 U/L (men) and 38 U/L (women), while Labcorp prints 65 and 60. Cohort studies, including NHANES III, link elevated GGT (defined there as above 51 U/L in men and 33 U/L in women) with higher all-cause mortality (hazard ratio 1.5, 95% CI 1.2–1.8), and with liver, cancer and diabetes deaths. These are associations, and no outcome-based target exists.
LOINC 2324-2 (primary). Specimen: serum-or-plasma.
Sources
- γ-Glutamyl Transferase (GGT) (test 001958), Labcorp
- Sample report, GGT (test 001958), Labcorp
- New IFCC reference procedures for the determination of catalytic activity concentrations of five enzymes in serum: preliminary upper reference limits obtained in hospitalized subjects, Clinica Chimica Acta (2003)
- Elevated serum alanine aminotransferase and gamma-glutamyltransferase and mortality in the United States population, Gastroenterology (2009)
- Gamma-Glutamyl Transferase (GGT) Blood Test, Cleveland Clinic (2024)
- Gamma-glutamyl Transferase (GGT) Test, MedlinePlus (National Library of Medicine)
- Gamma Glutamyl Transferase, Serum or Plasma (test 0020009), ARUP Laboratories
- Gamma-glutamyltransferase: friend or foe within?, Liver International (2016)
- Gamma glutamyl transferase, Critical Reviews in Clinical Laboratory Sciences (2001)
- Biochemical markers of alcoholism, Clinical Chemistry and Laboratory Medicine (2007)
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.