ALT (Alanine Aminotransferase)
ALT is an enzyme concentrated in liver cells that leaks into blood when hepatocytes are injured. It is the most liver-specific of the common transaminases and rises with fatty liver disease, viral hepatitis, alcohol use, medications (including statins and acetaminophen), and autoimmune or metabolic liver disease. Persistently elevated ALT warrants further evaluation.
Units: U/L. Check the units on your report before comparing to any range here.
Optimal range: who says what
Institutions, researchers and practitioners draw the line in different places. Each position is listed with who holds it and, where a document states it, a link. How we verify ranges.
- Institution or study29-33 U/L (men), 19-25 U/L (women)American College of Gastroenterology guideline (2017)The guideline calls this the true healthy normal range and says levels above it should be assessed
- Institution or study≤30 U/L (men), ≤19 U/L (women)Prati et al. 2002 (Ann Intern Med), 6,835 Milan blood donorsUpdated upper limits of normal, lower than the 40 (men) and 30 (women) limits then in use
- Named practitioner<33 U/L (men), <25 U/L (women)Optimal DX · Optimal GGT Levels: More Than a Liver Enzyme
- Named practitioner19-25 U/L (women), 29-33 U/L (men)Rupa Health · Interpreting Liver Enzyme Tests: ALT, AST, and ALP
- Lab reference interval4-36 U/L (MedlinePlus)What a lab report flags against. A lab interval is not an optimal target.
Practitioner targets are individual positions, often tighter than guideline ranges. Each was checked against its article before publishing.
21 of 21 itemized panels
Liver Function
What is ALT (Alanine Aminotransferase)?
ALT (Alanine Aminotransferase) is an enzyme found primarily in your liver cells. When liver cells are damaged or inflamed, ALT leaks into your bloodstream, making it one of the most specific and sensitive markers for liver cell injury.
Unlike other liver enzymes like AST (which is also found in heart and muscle tissue), ALT is highly concentrated in the liver, which makes it the most specific indicator of hepatocellular damage. This specificity makes ALT the go-to marker for detecting conditions like fatty liver disease, viral hepatitis, medication-induced liver injury, and other forms of liver inflammation.
ALT is typically measured as part of a comprehensive metabolic panel or liver function tests. While conventional reference ranges often extend up to 40-55 U/L, research shows that optimal levels for longevity and metabolic health are much lower, typically under 25-30 U/L for men and under 20-25 U/L for women.
Why ALT Is Your Most Important Liver Health Marker
- Most specific liver enzyme: ALT is predominantly found in liver cells, making it more specific for liver damage than AST or ALP
- Early detection of fatty liver: Even mildly elevated ALT (25-40 U/L) often indicates non-alcoholic fatty liver disease (NAFLD), which affects 25-30% of adults
- Metabolic health indicator: ALT correlates strongly with insulin resistance, obesity, and metabolic syndrome
- Cardiovascular risk marker: Elevated ALT predicts increased risk of heart disease, stroke, and type 2 diabetes
- Reversible with lifestyle: Unlike advanced liver disease, early ALT elevation can be normalized through diet, exercise, and weight loss
Interpretation bands (curated, PMID-backed)
Holder: OptimizeBiomarkers editorial synthesis of: Loss of Life Expectancy by 10 Years or More From Elevated Aspartate Aminotransferase: Finding Aspartate Aminotransferase a Better Mortality Predictor for All-Cause and Liver-Related than Alanine Aminotransferase (Xie et al., 2019); Serum aminotransferase activity and mortality risk in a United States community (Lee et al., 2008); Complex association between alanine aminotransferase activity and mortality in general population: a systematic review and meta-analysis of prospective studies (Liu et al., 2014). No single paper sets these cutoffs; for attributed targets see who says what.
Optimal (Longevity)Men: <25 U/L, Women: <20 U/L▼
- Associated with lowest metabolic disease risk and optimal liver health
- Studies show ALT below these levels correlates with reduced cardiovascular events, lower diabetes risk, and better overall longevity
- This is the target range for health optimization
Borderline ElevatedMen: 25-40 U/L, Women: 20-35 U/L▼
- Often still within "normal" lab range but indicates early metabolic dysfunction or mild fatty liver
- This range warrants lifestyle intervention, weight loss if overweight, and investigation of underlying causes
- Retest in 3-6 months after implementing changes
Moderately Elevated40-100 U/L▼
- Indicates significant liver inflammation or damage
- Common causes include NAFLD, alcohol consumption, viral hepatitis, or medication toxicity
- Requires medical evaluation, liver imaging (ultrasound), and investigation of underlying cause
- Consider checking AST, GGT, and hepatitis panel
Severely Elevated>100 U/L▼
- Indicates acute or severe liver injury
- Levels >1000 U/L suggest acute hepatitis (viral, drug-induced, or autoimmune) or ischemic liver injury
- Requires immediate medical attention, comprehensive liver workup including viral hepatitis panel, autoimmune markers, and imaging
- Very high levels (>10,000) can indicate acute liver failure
- Loss of Life Expectancy by 10 Years or More From Elevated Aspartate Aminotransferase: Finding Aspartate Aminotransferase a Better Mortality Predictor for All-Cause and Liver-Related than Alanine Aminotransferase.
- Serum aminotransferase activity and mortality risk in a United States community.
- Complex association between alanine aminotransferase activity and mortality in general population: a systematic review and meta-analysis of prospective studies.
What raises or lowers ALT
Causes of high ALT
- Non-alcoholic fatty liver disease (NAFLD/NASH): Most common cause, linked to obesity and insulin resistance
- Alcohol: Even moderate consumption can elevate ALT; heavy drinking causes alcoholic hepatitis
- Viral hepatitis: Hepatitis A, B, or C infection (can cause very high levels >500 U/L)
- Medications: Statins, antibiotics (especially augmentin), acetaminophen, NSAIDs, many others
- Autoimmune hepatitis: Body's immune system attacks liver cells
- Hemochromatosis: Iron overload damages liver (check ferritin and iron saturation)
- Wilson's disease: Copper accumulation in liver (rare, usually young adults)
- Celiac disease: Gluten sensitivity can cause mild ALT elevation
- Toxins: Industrial chemicals, herbal supplements, anabolic steroids
Causes of low ALT
- Vitamin B6 (pyridoxine) deficiency
- Chronic kidney disease with uremia
- Severe malnutrition or cachexia
- Genetic variants affecting ALT expression (very rare)
Symptoms when ALT is high or low
When high
- Fatigue and low energy (most common)
- Right upper quadrant abdominal discomfort or fullness
- Nausea or loss of appetite
- Dark urine (if bilirubin also elevated)
- Jaundice - yellowing of skin/eyes (only if liver function significantly impaired)
- Often asymptomatic: Many people with elevated ALT have no symptoms, which is why screening is important
Symptoms become more pronounced as ALT increases. Mild elevations (25-50 U/L) often cause subtle fatigue or no symptoms, while severe elevations (>200 U/L) typically cause more obvious symptoms and warrant urgent evaluation.
When low
Low ALT is uncommon and generally not clinically significant. Possible associations include:
- Vitamin B6 deficiency (ALT requires B6 as cofactor)
- Kidney disease (especially hemodialysis patients)
- Rare genetic conditions
- Very low protein intake or malnutrition
Low ALT rarely requires treatment unless part of broader nutritional deficiency. Focus on balanced diet with adequate protein and consider B6 supplementation (50-100 mg daily) if deficient.
How to move ALT
Effect sizes (how much something moves the marker) appear only where the paper cited under the item states them. Talk to your clinician before starting or changing any medication or supplement.
Weight Loss and Dietary Changes
- Mediterranean diet: Emphasize olive oil, fish, vegetables, whole grains. Losing 5-10% of body weight often brings ALT back into range
- Reduce refined carbohydrates and sugar: Limit fructose, high-fructose corn syrup, white bread, and sugary drinks
- Increase protein intake: 1.2-1.6 g/kg body weight supports lean mass during weight loss
- Intermittent fasting: Time-restricted eating (16:8) or alternate-day fasting can improve fatty liver
- Coffee: 2-3 cups daily associated with lower ALT and reduced liver fibrosis risk
Exercise and Physical Activity
- Aerobic exercise: 150-300 minutes/week of moderate intensity (brisk walking, cycling, swimming)
- Resistance training: 2-3 sessions/week builds muscle mass and improves insulin sensitivity
- High-intensity interval training (HIIT): Particularly effective for reducing liver fat
- Exercise works even without weight loss: Physical activity independently improves ALT and liver fat content
Target Insulin Resistance and Metabolic Health
- Metformin: 500-2000 mg daily (if diabetic or prediabetic) improves insulin sensitivity and may reduce liver fat
- GLP-1 agonists: Semaglutide, liraglutide show significant benefits for NAFLD and ALT reduction
- Berberine: 500 mg 2-3x daily, natural insulin sensitizer with liver-protective effects
- Optimize sleep: 7-9 hours nightly; poor sleep worsens insulin resistance and fatty liver
- Manage stress: Chronic stress elevates cortisol, which promotes abdominal fat and liver fat accumulation
Liver-Protective Supplements
- Vitamin E: 400-800 IU daily (mixed tocopherols) reduces ALT in NAFLD (works best if non-diabetic)
- Omega-3 fatty acids: 2-4g EPA+DHA daily reduces liver fat and inflammation
- Milk thistle (silymarin): 140-280 mg 2-3x daily supports liver regeneration
- N-acetylcysteine (NAC): 600-1200 mg daily boosts glutathione, a key liver antioxidant
- Choline: 550 mg daily (or phosphatidylcholine) prevents fat accumulation in liver
Eliminate Hepatotoxins
- Limit or eliminate alcohol: Even moderate drinking (1-2 drinks daily) can elevate ALT and accelerate liver disease
- Review medications: Statins, NSAIDs, antibiotics, and many supplements can cause drug-induced liver injury
- Avoid excessive acetaminophen: Stay under 3000 mg/day; lower if drinking alcohol or taking other medications
- Reduce toxin exposure: Minimize pesticides, industrial chemicals, and unnecessary supplements
- Check for viral hepatitis: Test for Hepatitis B and C if ALT remains elevated despite lifestyle changes
When to retest
- After lifestyle changes: Retest ALT after 8-12 weeks of diet, exercise, and weight loss interventions to assess response
- After medication changes: If starting a new medication that might affect liver, retest in 4-8 weeks
- If moderately elevated (40-100 U/L): Retest every 3-6 months until normalized, along with AST, GGT, and potentially liver ultrasound
- If severely elevated (>100 U/L): Retest within 2-4 weeks along with comprehensive liver panel (AST, ALP, bilirubin, albumin, PT/INR) and hepatitis screening
- Annual screening: If you have metabolic risk factors (obesity, diabetes, metabolic syndrome), check ALT annually even if previously normal
Scientific Evidence
Lower ALT Limits Find More Liver Disease
In 6,835 first-time blood donors at low risk of liver disease, healthy upper limits for ALT were 30 U/L for men and 19 U/L for women, below the conventional 40 and 30 U/L. The lower limits picked up hepatitis C viremia with 76% sensitivity versus 55%, at a specificity of 88.5% versus 97.4%.
Source: Updated definitions of healthy ranges for serum alanine aminotransferase levels.
ALT and Cardiovascular Risk
In 6,899 adults followed for 10.5 years (PREVEND), higher ALT was associated with slightly lower, not higher, cardiovascular risk (HR 0.88 per standard deviation after full adjustment). Adding ALT to standard risk factors did not improve cardiovascular risk prediction.
Weight Loss Reverses Fatty Liver
In 293 patients with biopsy-proven NASH given lifestyle advice for 52 weeks, 30% lost at least 5% of body weight. Among those who lost 10% or more, all had lower disease activity scores, 90% had NASH resolution and 45% had fibrosis regression.
Which Providers Test ALT (Alanine Aminotransferase)?
Cheapest: Oura Health Panels at $99/year. Most comprehensive: Function Health, 160+ biomarkers for $365/year.
21 panels that include it, cheapest first
| Provider | Annual Cost | Total Biomarkers | $/Biomarker |
|---|---|---|---|
| $99 | 50 | $1.98 | |
| $190 | 100+ | $1.90 | |
| $250 | 65 | $3.85 | |
| $297 | 100+ | $2.97 | |
 Labcorp OnDemand | $338 | 50+ | $6.76 |
 Superpower | $349 | 100+ | $3.49 |
| $349 | 75+ | $4.65 | |
 WHOOP Advanced Labs | $349 | 65 | $5.37 |
 Function Health | $365 | 160+ | $2.28 |
| $365 | 100+ | $3.65 | |
| $375 | 108 | $3.47 | |
| $449 | 83 | $5.41 | |
| $495 | 80+ | $6.19 | |
| $499 | 100+ | $4.99 | |
| $700 | 138 | $5.07 | |
| $829 | 54 | $15.35 | |
| $895 | 100+ | $8.95 | |
| $996 | 59 | $16.88 | |
| $1188 | 70+ | $16.97 | |
| $1198 | 40+ | $29.95 | |
| $1950 | 130+ | $15.00 |
$/Biomarker is annual cost divided by the panel's advertised biomarker count, not the price of this one test. We track 23 blood test providers (32 plans); 21 of those plans are itemized marker by marker. Compare all of them.
11 providers not itemized in our matrix
We have not itemized these marker by marker (some sell tests one at a time), so this page cannot say whether they offer ALT (Alanine Aminotransferase). Check with them directly.
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Experts discussing ALT (Alanine Aminotransferase)
Podcast episodes where clinicians and researchers cover this marker in depth. Curated by hand; an episode is listed only when the marker is a substantial topic, not a passing mention.
- How Insulin Resistance Drives Fatty Liver, Cognitive Issues, and Metabolic SyndromeDisclosure: Hyman co-founded Function Health, which appears in our blood-test comparisons.
- The Best Diet to Reverse Fatty Liver DiseaseDisclosure: Hyman co-founded Function Health, which appears in our blood-test comparisons.
- What's the Deal with Liver Enzymes with Dr. William Carey MD
- Liver Function Testing - What Every Question You've Ever Had
Frequently Asked Questions
What is the optimal range for ALT (Alanine Aminotransferase)?
Published positions differ: 29-33 U/L (men), 19-25 U/L (women) (American College of Gastroenterology guideline (2017)); ≤30 U/L (men), ≤19 U/L (women) (Prati et al. 2002 (Ann Intern Med), 6,835 Milan blood donors). Named practitioners target: <33 U/L (men), <25 U/L (women) (Optimal DX); 19-25 U/L (women), 29-33 U/L (men) (Rupa Health). Lab reference interval: 4-36 U/L (MedlinePlus). That is what a lab report flags against, not an optimal target.
Which blood test providers include ALT (Alanine Aminotransferase)?
21 of the 21 blood testing panels we itemize marker by marker include ALT (Alanine Aminotransferase) in their panels. This biomarker is widely available across major providers.
Related: YouBoost rates lifestyle and supplement interventions by evidence.
Medical Disclaimer
This information is for educational purposes only and is not medical advice. Always consult with a qualified healthcare provider about your specific health needs.
Last reviewed Sep 23, 2026 · First published Sep 30, 2025