γ-Glutamyl Transferase (GGT) Test
γ-Glutamyltransferase (GGT) Test
Key Points
- Primary marker of hepatobiliary disease
- Sensitive indicator of alcohol-induced liver injury
- Important in drug metabolism pathways
- Age and gender-specific reference ranges
- Essential component of liver function panels
Overview
GGT is a membrane-bound enzyme present in:
- Hepatocytes and biliary epithelial cells
- Renal tubules
- Pancreas
- Intestine
- Brain tissue
Molecular Characteristics
- Enzyme Structure:
- Type I membrane glycoprotein
- Molecular weight: 68 kDa
- Active site faces extracellular space
- Multiple isoforms exist
- Physiological Functions:
- Glutathione metabolism
- Xenobiotic detoxification
- Amino acid transport
- Antioxidant defense
- Cell membrane protection
Metabolic Pathways
- γ-Glutamyl Cycle:
- Glutathione synthesis and breakdown
- Amino acid transport
- Cellular redox status regulation
- Drug Metabolism:
- Phase II conjugation reactions
- Detoxification processes
- Drug-induced enzyme induction
Primary Clinical Indications
Hepatobiliary Disorders
- Cholestatic Conditions:
- Biliary atresia
- Choledochal cyst
- Progressive familial intrahepatic cholestasis
- Sclerosing cholangitis
- Hepatocellular Disease:
- Viral hepatitis
- Drug-induced liver injury
- Metabolic liver disease
- Autoimmune hepatitis
Other Applications
- Medication Monitoring:
- Anticonvulsant therapy
- Chemotherapy
- Immunosuppressants
- Screening:
- Asymptomatic liver disease
- Metabolic syndrome
- Pancreatic disorders
Testing Methods
Sample Requirements
- Specimen Type:
- Serum (preferred)
- Heparinized plasma
- Minimum volume: 0.5 mL
- Collection Conditions:
- Fasting not required
- Morning collection preferred
- Stable for 7 days at 4°C
Analytical Techniques
- Enzymatic Methods:
- Spectrophotometric assay
- Kinetic measurement
- IFCC standardized method
- Quality Assurance:
- Daily calibration
- Temperature control
- Reference material standardization
Reference Ranges
Age-Specific Values (U/L)
- Newborns (0-7 days):
- Male: 45-250
- Female: 40-240
- Infants (1-12 months):
- Male: 8-90
- Female: 8-80
- Children (1-12 years):
- Male: 5-32
- Female: 5-24
- Adolescents (13-18 years):
- Male: 7-42
- Female: 7-32
Pattern Recognition
- Isolated GGT Elevation:
- Medication effect
- Early biliary disease
- Enzyme induction
- Combined Elevations:
- GGT + ALP: Cholestasis
- GGT + Transaminases: Hepatocellular injury
- GGT + Bilirubin: Conjugated hyperbilirubinemia
Developmental Changes
- Neonatal Period:
- Physiologically elevated
- Rapid changes in first week
- Correlation with gestational age
- Infancy:
- Gradual decline to childhood range
- Important in biliary atresia workup
- Monitor during parenteral nutrition
Special Populations
- Premature Infants:
- Higher baseline values
- Slower normalization
- Different reference ranges
- Adolescents:
- Gender differences emerge
- Impact of hormonal changes
- Body mass effects
Specific Disease Patterns
- Biliary Tract Disease:
- Early marker of obstruction
- Progressive elevation pattern
- Correlation with imaging findings
- Drug-Induced Liver Injury:
- Pattern recognition
- Monitoring intervals
- Recovery assessment
Monitoring Guidelines
- Frequency of Testing:
- Acute conditions: Daily to weekly
- Chronic conditions: Monthly to quarterly
- Medication monitoring: As per protocol
- Treatment Response:
- Expected timeline for improvement
- Indicators of recovery
- Red flags for deterioration
Research Applications
- Biomarker Development:
- Novel disease markers
- Prognostic indicators
- Treatment response prediction
- Clinical Trials:
- Safety monitoring
- Efficacy assessment
- Protocol development
Future Directions
- Emerging Applications:
- Metabolic syndrome screening
- Cardiovascular risk assessment
- Cancer surveillance
- Technical Advances:
- Point-of-care testing
- Novel analytical methods
- Automated interpretation systems
