Apr 15, 2025
ALT vs GGT: Key Differences Explained
Compare ALT and GGT to learn which marker is more relevant for health assessment.
Introduction
Alanine Transaminase (ALT) and Gamma-Glutamyl Transferase (GGT) are liver enzymes commonly used in liver function tests. While both are markers of liver health, they serve distinct roles in identifying liver damage, bile flow issues, and alcohol-related liver disease. This guide compares ALT and GGT to help you interpret your lab results effectively.
What Is ALT?
Alanine Transaminase (ALT) is an enzyme found primarily in liver cells. It enters the bloodstream when liver cells are damaged. Elevated ALT levels are a sensitive indicator of liver inflammation or injury, often seen in hepatitis, fatty liver disease, or medication toxicity.
What Is GGT?
Gamma-Glutamyl Transferase (GGT) is involved in glutathione metabolism and is present in liver, bile ducts, and pancreas. High GGT levels typically signal issues with bile flow or chronic alcohol use, even when other liver enzymes are normal.
Comparison Table
Criteria | ALT | GGT |
|---|---|---|
Primary Function | Detects liver cell injury | Indicates bile duct issues and alcohol-related liver damage |
Diagnostic Relevance | Useful in liver inflammation (hepatitis, fatty liver) | Useful in bile flow obstruction, alcohol use disorders |
Speed of Response | Elevates rapidly after liver damage | Increases steadily with bile or alcohol issues |
Specificity | High specificity for liver damage | Less specific, can be elevated from multiple causes |
Clinical Use | Screening and monitoring liver inflammation | Assessing alcohol intake or cholestasis |
Measurement Units | U/L | U/L |
Normal Range | 7–56 U/L | 9–48 U/L |
Best Use Case | Detecting general liver inflammation | Confirming alcohol-related damage or biliary blockage |
Clinical Use Cases
ALT is typically used to identify liver damage from viral hepatitis, non-alcoholic fatty liver disease (NAFLD), or medication toxicity. GGT is used to detect bile duct problems or alcohol-related liver injury, especially when ALT and AST are normal.
Which Test Should You Choose?
If you're assessing general liver function or inflammation, ALT is your go-to marker. If alcohol intake, bile flow, or medication-induced stress is suspected, GGT offers better specificity for these concerns.
Using Both Together
ALT and GGT are often ordered together in liver panels. When both are elevated, it may suggest dual pathology—such as alcohol-related liver damage alongside hepatitis. If GGT is elevated but ALT is normal, it may indicate early bile obstruction or alcohol use without hepatocellular injury.
Pros and Limitations
ALT Pros: Highly sensitive to hepatocellular damage
ALT Limitations: May miss early bile duct issues or chronic alcohol use
GGT Pros: Excellent for detecting cholestasis and alcohol-related stress
GGT Limitations: Less specific—can be elevated in kidney disease, heart disease, or by some medications
When to Test
ALT and GGT may be tested when symptoms like fatigue, jaundice, or right upper quadrant pain occur. They are also used to monitor known liver conditions or evaluate the effects of alcohol or certain medications on liver health.
FAQs
Can ALT be high and GGT normal?
Yes, in cases of isolated liver inflammation like viral hepatitis without bile obstruction.
What if GGT is high but ALT is normal?
This could suggest alcohol use, early cholestasis, or enzyme induction from medications.
Do these levels normalize after treatment?
Both enzymes often return to normal with treatment and lifestyle changes if the underlying cause is addressed.