Gamma-Glutamyl Transferase
GGT· also: Gamma GT, GGTP
Clinical Overview
GGT is an enzyme found primarily in the liver, pancreas, and kidneys. It is the most sensitive marker of liver disease and alcohol consumption. GGT is elevated in virtually all liver disorders and is used to determine whether elevated ALP is of liver or bone origin.
Why This Test Matters
GGT is the most sensitive liver enzyme — it is elevated before other markers in early liver disease. Its primary clinical value is as a complementary test: when ALP is elevated, an elevated GGT confirms a liver source. It is also used as a surrogate marker of alcohol consumption, as chronic alcohol use elevates GGT even in the absence of structural liver disease. Cardiovascular risk correlates with GGT levels.
Reference RangesWHO/IFCC standards
| Age Group | Sex | Reference Range | Unit | Notes |
|---|---|---|---|---|
| Adults (18–64) | Male | 8 – 61 | U/L | — |
| Adults (18–64) | Female | 5 – 36 | U/L | — |
Also reported in: IU/L.
What Causes Abnormal Results?
High GGT Causes
- Alcohol use (even without liver disease)
- Non-alcoholic fatty liver disease (NAFLD)
- Cholestatic liver disease (bile duct obstruction, primary biliary cholangitis)
- Medications: anticonvulsants (phenytoin, carbamazepine), warfarin, statins, antidepressants
- Chronic pancreatitis
- Diabetes mellitus
- Hyperthyroidism
- Renal failure
Low GGT Causes
- Not clinically significant
- Hypothyroidism (can slightly lower GGT)
Signs & Symptoms to Watch For
How to Prepare for This Test
Fasting is not strictly required but preferred. Avoid alcohol for at least 24 hours before testing to accurately assess baseline GGT. Inform your doctor of all medications.
Factors That Can Affect Results
- Alcohol consumption (raises GGT even in moderate amounts)
- Numerous medications (phenytoin, carbamazepine, warfarin, statins)
- Obesity (independently raises GGT)
- Smoking (mild elevation)
Related Topics
Frequently Asked Questions
Can GGT be used to detect alcohol use?
GGT is commonly elevated in people who drink alcohol regularly, even in amounts not causing structural liver damage. It rises within weeks of regular drinking and falls within 2–4 weeks of abstinence. However, it is not specific for alcohol — medications and liver disease also raise GGT. It is best used in combination with other markers (MCV, transferrin desaturation) rather than alone.
Why is GGT elevated when taking anticonvulsant medications?
Drugs like phenytoin and carbamazepine are potent enzyme inducers — they stimulate liver enzymes including GGT to increase production, even without causing liver cell damage. This is a pharmacological effect, not liver disease. GGT elevation from enzyme-inducing drugs is an isolated finding without corresponding ALT or bilirubin elevation.