Unit Converter
Gamma Glutamyltransferase (GGT)
(Key Liver–Biliary Enzyme – Marker for Cholestasis, Alcohol Use, Drug Toxicity & NAFLD)
Synonyms
- GGT
- γ-GT
- Gamma-glutamyltransferase
- γ-Glutamyl transpeptidase
- Glutamyltransferase
Units of Measurement
Enzyme activity may be reported as:
- nkat/L
- µkat/L
- nmol/(s·L)
- µmol/(s·L)
- U/L
- IU/L
- µmol/(min·L)
- µmol/(h·L)
- µmol/(h·mL)
Unit Conversions
1 U/L = 1 IU/L
1 U/L = 16.67 nkat/L
1 nkat/L = 0.06 U/L
1 µmol/(min·L) = 60 U/L
1 µmol/(h·L) = 1 U/L
1 nmol/(s·L) = 1 µkat/L = 1 U/L × 1/16.67
Description
Gamma-glutamyltransferase (GGT) is a membrane-bound enzyme found predominantly in:
- Liver (highest concentration)
- Bile ducts
- Pancreas
- Kidney
- Spleen
- Intestine
It plays a key role in glutathione metabolism and amino-acid transport.
Serum GGT is one of the most sensitive indicators of hepatobiliary disease, particularly cholestasis and alcohol use.
Physiological Role
GGT transfers γ-glutamyl groups from glutathione to amino acids — involved in:
- Glutathione recycling
- Antioxidant defense
- Cellular detoxification
The enzyme is easily induced by alcohol and drugs.
Clinical Significance
High GGT (Most Common Finding)
1. Hepatobiliary Disease
GGT rises early and significantly in:
- Cholestasis (obstruction)
- Bile duct disease
- Primary biliary cholangitis
- Primary sclerosing cholangitis
- Gallstones
- Biliary strictures
2. Alcohol Use
- GGT is highly inducible by ethanol
- Chronic alcohol intake → persistent elevation
- Used to monitor alcohol abstinence
3. Non-Alcoholic Fatty Liver Disease (NAFLD)
- Mild–moderate GGT elevation common
- Correlates with insulin resistance & metabolic syndrome
4. Drug-Induced Liver Injury
Increased with:
- Phenytoin
- Carbamazepine
- Barbiturates
- Statins
- Alcohol
- Rifampicin
5. Pancreatic Disease
- Pancreatitis
- Pancreatic duct obstruction
6. Cardiovascular Risk Marker
High GGT is linked with:
- Increased CVD mortality
- Oxidative stress burden
Low or Normal GGT
Generally clinically insignificant.
Useful to distinguish:
- Bone ALP elevation (GGT normal)
vs. - Liver ALP elevation (GGT high)
Reference Intervals
(Tietz 8E + Mayo + ARUP + AASLD)
Ranges vary by sex and age due to enzyme induction.
Adult Men
- 10 – 71 U/L
Adult Women
- 6 – 42 U/L
Children
GGT higher in early infancy; adult ranges apply by adolescence.
Severe Elevation
- >300 U/L → cholestasis, bile duct obstruction
- >1000 U/L → severe cholangitis or obstruction
Diagnostic Uses
1. Differentiating Source of ALP Elevation
- ALP ↑, GGT ↑ → hepatic / biliary source
- ALP ↑, GGT normal → bone source
2. Screening for Chronic Alcohol Use
- Elevated GGT is sensitive but not specific
- Used with CDT (carbohydrate-deficient transferrin)
3. Primary Biliary Diseases
- High GGT with high ALP
- Hallmark of cholestatic disorders
4. Assessing Drug Toxicity
Monitor patients on:
- Antiepileptics
- Alcohol
- Rifampicin
- Statins
5. NAFLD & Metabolic Syndrome
GGT elevation correlates with:
- Insulin resistance
- Obesity
- Diabetes
- Hypertension
Analytical Notes
- Serum sample
- Hemolysis: minimal effect
- Highly inducible enzyme → interpret with clinical context
- Avoid heavy alcohol intake 48 hours before testing
- Age and sex influence values
- Fasting not required
Clinical Pearls
- GGT is one of the earliest markers to rise in cholestasis.
- Normal GGT with high ALP → bone origin (Paget’s disease, fractures).
- Alcohol elevates GGT more than AST/ALT early on.
- GGT combined with ALP helps differentiate obstructive vs hepatocellular patterns.
- Very high GGT (>1000 U/L) seen in obstructive jaundice & cholangitis.
Interesting Fact
GGT plays a critical role in glutathione metabolism, making it an important marker for oxidative stress beyond liver disease.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Enzymes.
- AASLD / ACG / EASL Guidelines - Liver Function Testing.
- Mayo Clinic Laboratories - GGT.
- ARUP Consult - Hepatic Enzymes.
- IFCC Standard Enzyme Units.
- MedlinePlus / NIH - GGT Test.