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Gamma Glutamyl Transferase

Immunology & Autoimmune

Gamma-glutamyltransferaseGamma-glutamyl transpeptidaseGGT

Review status

Currently under review

Pending specialist review and validation.

What it shows

Gamma glutamyl transferase is an enzyme found in the lining of the bile ducts and in many tissues, especially the liver. A blood test measures the activity of this enzyme circulating in your blood.

Because this enzyme responds to changes in bile flow and to certain substances, it is often checked together with other liver tests such as ALT, AST, alkaline phosphatase, and bilirubin. Your result helps build a fuller picture of liver and bile duct health rather than providing a stand-alone diagnosis.

Why it matters

This test helps evaluate problems that affect the liver and bile ducts. When alkaline phosphatase is elevated, a raised GGT supports a liver or bile duct source rather than bone. It can also increase with fatty liver, viral hepatitis, alcohol use, medication effects, and some pancreatic or gallbladder conditions.

Clinicians order GGT if you have symptoms that suggest liver or biliary issues, if other liver tests are abnormal, or to monitor the impact of medicines or alcohol on liver health. The result does not identify a single cause on its own, but it helps guide next steps in testing and treatment.

Understanding your results

Your GGT is interpreted alongside your history, examination, and other labs. A higher value may point to bile duct irritation or blockage, liver inflammation, medication effects, or alcohol exposure. A value in the expected range is reassuring, but no single test can rule out every liver condition.

If your result is unexpectedly high, your clinician may repeat the test, review medicines and supplements, discuss alcohol intake, and consider imaging or other blood tests. If alcohol is a contributor, reducing or stopping use often helps. Low values are usually not worrisome and typically do not require action.

Reference ranges

30 – 204 U/L
Female
0 days – 6 days
30 – 204 U/L
Male
0 days – 6 days
14 – 113 U/L
Female
6 days – 3 months
14 – 114 U/L
Male
6 days – 3 months
11 – 32 U/L
Female
3 months – 11 months
11 – 32 U/L
Male
3 months – 11 months
8 – 18 U/L
Female
11 months – 3 years
8 – 18 U/L
Male
11 months – 3 years
11 – 23 U/L
Female
3 years – 10 years
11 – 23 U/L
Male
3 years – 10 years
0 – 40 U/L
Female
10 years – 18 years
0 – 40 U/L
Male
10 years – 18 years
7 – 50 U/L
Female
18 years – 150 years
7 – 50 U/L
Male
18 years – 150 years

Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.

Factors that could impact Gamma Glutamyl Transferase

  • Recent alcohol intake

    Alcohol can increase GGT activity, sometimes even after short-term use. Avoid drinking before testing if your clinician advises, and share an accurate alcohol history for proper interpretation.

  • Medications and supplements

    Certain drugs such as phenytoin, phenobarbital, carbamazepine, rifampin, and some herbal products can raise GGT by inducing liver enzymes. Always list prescriptions, over-the-counter products, and supplements.

  • Metabolic health and fatty liver

    Obesity, insulin resistance, and nonalcoholic fatty liver disease can be associated with higher GGT. Lifestyle changes that improve metabolic health may help bring levels down over time.

  • Smoking

    Cigarette smoking can increase GGT through enzyme induction. If you smoke, tell your clinician, as this may influence interpretation and follow-up plans.

  • Age and sex

    Expected values vary by age and sex due to developmental and hormonal differences. Pediatric and adult reference intervals are not the same, and your report accounts for this.

  • Pregnancy and cholestasis

    GGT is often normal in pregnancy, but conditions that impair bile flow, such as intrahepatic cholestasis of pregnancy, can increase it. Tell your clinician if you are pregnant or recently postpartum.

  • Pre-test preparation and handling

    Fasting is usually not required. Provide a good history of recent alcohol use and medications. Proper sample handling helps ensure accurate enzyme activity measurement.

2026

References

  1. McGill University Health Centre. (2014, May 28). Gamma Glutamyl Transferase (Task CD 316524). Laboratory reference ranges.
  2. Kwo, P. Y., Cohen, S. M., & Lim, J. K. (2017). ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries. The American Journal of Gastroenterology, 112(1), 18–35.
  3. Whitfield, J. B. (2001). Gamma glutamyl transferase. Critical Reviews in Clinical Laboratory Sciences, 38(4), 263–355.