Liver Enzymes Explained: ALT, GGT, and AST — What Your Bloodwork Actually Means

You got your blood results back. ALT is flagged. Or GGT. Or both. The reference range says “normal” is under 40 U/L and yours is 67. Your doctor said to “keep an eye on it” and follow up in three months.

Now what?

This page explains what these three liver enzymes actually measure, what elevated levels mean and don’t mean, and what you can do about them.

This article is for educational purposes only. Elevated liver enzymes require physician evaluation — this content does not substitute for medical advice.

The Three Main Liver Enzymes and What They Measure

Liver enzymes are proteins that perform specific chemical reactions inside liver cells. When liver cells are damaged or stressed, their membranes become permeable and enzymes leak into the bloodstream — which is why elevated levels in a blood test indicate liver cell stress or injury.

ALT — Alanine Aminotransferase

What it is: An enzyme involved in amino acid metabolism. Present in high concentrations in the liver, with smaller amounts in kidney, heart, and muscle.

What elevation means: ALT is the most liver-specific of the three enzymes. Elevated ALT is a relatively specific signal that liver cells are damaged or stressed. ALT elevation is the primary biomarker used to assess liver injury in clinical settings.

Normal range: Typically 7–56 U/L in men, 7–45 U/L in women (ranges vary slightly by laboratory). Some research suggests the upper limit of normal should be lower — ~30 U/L for men, ~19 U/L for women — to catch earlier stages of liver disease.

What causes elevated ALT:

MASLD/NAFLD (most common cause of mild-moderate elevation in the general population)
Alcohol-related liver disease
Viral hepatitis (A, B, C) — can produce dramatic elevations (10–50x normal)
Medication toxicity (statins, acetaminophen, some antibiotics)
Autoimmune hepatitis
Celiac disease (less commonly known association)
Vigorous exercise (ALT can be mildly elevated post-exercise due to muscle ALT)

The magnitude matters:

Mild elevation (1–3x normal): Most commonly MASLD, alcohol, or benign causes. Not urgent but worth investigating.
Moderate elevation (3–10x normal): More concerning. MASLD, alcohol, medications.
Marked elevation (>10x normal): Suggests acute liver injury — viral hepatitis, drug toxicity, ischemia. Requires prompt evaluation.

GGT — Gamma-Glutamyl Transferase

What it is: An enzyme involved in glutathione metabolism and amino acid transport, present on cell membranes in the liver, bile ducts, kidney, and pancreas.

What elevation means: GGT is the most sensitive marker for alcohol-related liver disease and is elevated in essentially all forms of significant liver pathology. However, it is less specific than ALT — GGT is elevated by many things, including alcohol, medications, and non-liver conditions.

Normal range: Approximately 9–48 U/L in men, 9–36 U/L in women (varies significantly by lab and age — GGT tends to increase with age).

GGT’s unique relationship with alcohol: GGT is the enzyme most reliably elevated by alcohol consumption. Even moderate social drinking over weeks to months can produce GGT elevation without significant ALT changes. This makes GGT a sensitive (though not specific) marker of alcohol intake — sometimes used in occupational medicine and clinical settings to assess drinking patterns.

Why GGT rises with alcohol:

Ethanol induces microsomal enzyme activity, including GGT production in liver cells
Acetaldehyde directly damages biliary epithelial cells, releasing GGT
Oxidative stress from alcohol metabolism upregulates GGT expression

Important: A single night of heavy drinking can elevate GGT measurably. Two to four weeks of abstinence typically normalizes GGT if alcohol is the only cause. If GGT remains elevated after 4 weeks of abstinence, other causes should be investigated.

The 2026 MASLD trial finding: The DHM intervention significantly reduced GGT in the treatment group vs. placebo after 12 months — supporting DHM’s mechanism of reducing alcohol-induced and metabolic liver stress at a biomarker level.

AST — Aspartate Aminotransferase

What it is: An enzyme involved in amino acid metabolism. Present in the liver but also in significant amounts in heart muscle, skeletal muscle, red blood cells, and kidney.

What elevation means: AST is less liver-specific than ALT. Elevated AST alone (without ALT elevation) more often reflects cardiac or muscle injury than liver disease.

Normal range: Approximately 10–40 U/L (less variation by sex than ALT or GGT).

The AST:ALT ratio: Clinically useful diagnostic tool:

AST:ALT < 1 (ALT higher than AST): Typical pattern in MASLD and viral hepatitis
AST:ALT > 2 (AST more than double ALT): Strongly suggests alcohol-related liver disease (the “De Ritis ratio” >2 in the alcohol context)
Very high AST with normal-mildly elevated ALT: Consider cardiac causes, rhabdomyolysis, or hemolysis

If your bloodwork shows elevated AST with normal ALT, liver disease is less likely as the primary cause.

Reading Your Results: A Practical Guide

Pattern	Most Likely Cause	Next Steps
Mild ALT elevation (1.5–3x), normal GGT	MASLD, early	Lifestyle assessment, repeat in 3–6 months
ALT elevated + GGT elevated	Alcohol, MASLD, medications	Assess alcohol intake, medications, consider ultrasound
GGT elevated, normal ALT	Recent/regular alcohol, medication effect	Reduce alcohol 4 weeks, recheck
AST:ALT ratio >2	Alcohol-related liver disease	Reduce/eliminate alcohol, follow up
Any enzyme >10x normal	Acute liver injury	Prompt medical evaluation
All three elevated, symptoms present	Multiple causes possible	Urgent physician evaluation

Factors That Affect Your Results (and Are Not Liver Disease)

Exercise: Vigorous physical activity — particularly resistance training, endurance exercise, or contact sports — can elevate ALT (mildly) and AST (significantly) due to muscle enzyme release. If you worked out the day before your blood draw, AST elevation is likely muscle-related.

Timing relative to drinking: GGT is sensitive to recent alcohol consumption. If you had drinks the week before your blood draw, your GGT may be temporarily elevated even if your baseline is normal.

Medications: Statins, metformin, certain antibiotics (amoxicillin-clavulanate), NSAIDS, and many others can elevate liver enzymes. If you’re on any medications, this should be assessed before concluding liver disease is the cause.

Body mass: Elevated BMI correlates with higher baseline liver enzymes even in the absence of MASLD — simply having more adipose tissue increases baseline metabolic liver stress.

What a Supplement Can and Can’t Do for Liver Enzymes

Elevated liver enzymes indicate liver cell stress. Reducing that stress — by reducing alcohol intake, losing weight, treating underlying metabolic disease — is what brings enzyme levels down.

Supplements with documented liver enzyme reduction in clinical trials:

DHM (dihydromyricetin): The 2026 MASLD RCT showed statistically significant ALT and GGT reduction vs. placebo over 12 months at 300mg/day. This is the strongest recent human RCT for any supplement in the liver enzyme category.

Milk thistle (silymarin): Multiple meta-analyses confirm ALT reduction in chronic liver disease populations. Effect size varies but is generally 10–25% reduction in mild-to-moderately elevated ALT.

Vitamin E: Multiple RCTs show ALT reduction in MASH specifically, though concerns about long-term use at high doses limit enthusiasm.

What supplements can’t do: reverse established cirrhosis, treat viral hepatitis, or substitute for managing the underlying metabolic condition driving MASLD.

→ Liver Health Supplements: What Actually Works → → What Is MASLD/NAFLD? → → DHM Liver Health Study: 2026 RCT →

When to See a Doctor (Don’t Wait on These)

Any liver enzyme >10x the upper limit of normal
Elevated enzymes plus symptoms: jaundice (yellow skin/eyes), right upper quadrant pain, dark urine, pale stool, significant fatigue
Elevated enzymes that don’t normalize after 4–6 weeks of lifestyle changes
Elevated enzymes plus known risk factors for liver disease (heavy alcohol use, viral hepatitis exposure, family history)
Any combination of elevated enzymes plus other abnormal results (elevated bilirubin, elevated INR/PT)

Mild enzyme elevation (1–2x normal) without symptoms and with clear modifiable cause (recent heavy drinking, new medication, recent intense exercise) can reasonably be rechecked in 4–8 weeks after addressing the cause. But “keep an eye on it” shouldn’t mean ignoring it — it means actually following up.