High Liver Enzymes (ALT & AST): What They Mean and What to Do
ALT and AST are the most commonly elevated markers on a standard blood panel. They often appear with a flag but little explanation. Here's what they actually mean, what causes elevation, and when to act.
See how your liver markers score against optimal ranges — free, instant, no account.
Upload My Report →What ALT and AST actually are
ALT (alanine aminotransferase) and AST (aspartate aminotransferase) are enzymes found inside liver cells (hepatocytes). Under normal conditions, they do their job quietly within the cell and only small amounts leak into the bloodstream. When liver cells are damaged or inflamed, they release these enzymes in larger quantities — causing elevated blood levels.
ALT is more liver-specific: it's found predominantly in the liver, which makes it a cleaner signal for liver injury. AST is found in multiple tissues — including the heart, skeletal muscle, kidneys, and red blood cells — so an elevated AST without elevated ALT might originate outside the liver entirely.
The ratio of AST to ALT (the AST/ALT ratio) can help identify the cause of elevation, which is why both are usually measured together as part of a liver function panel.
The ALT and AST ranges
| Level | ALT (U/L) | AST (U/L) | Interpretation |
|---|---|---|---|
| Optimal | < 25 (men) / < 19 (women) | < 25 | Lowest metabolic risk. Associated with optimal liver fat. |
| Normal / Acceptable | 25–40 (men) / 19–35 (women) | 25–40 | Within lab range. Mild elevation may still indicate early liver fat accumulation. |
| Mildly Elevated | 40–120 | 40–120 | Warrants investigation. Most commonly fatty liver, alcohol, or medication effect. |
| Moderately Elevated | 120–400 | 120–400 | More significant liver injury. Hepatitis, NASH, or drug-induced injury possible. Prompt follow-up needed. |
| Severely Elevated | > 400 | > 400 | Serious liver injury. Acute hepatitis, ischaemia, or toxicity. Urgent medical evaluation required. |
Reference ranges vary slightly by lab. Values in U/L. Optimal thresholds from AASLD and metabolic health literature.
ALT <19 (women)
Usually lifestyle
Prompt follow-up
Urgent evaluation
Common Causes of Elevated ALT and AST
The vast majority of mildly elevated ALT and AST results in otherwise well people have one of these causes:
The AST/ALT ratio — what it tells you
The ratio of AST to ALT can help identify the source of injury:
| AST/ALT ratio | Likely pattern |
|---|---|
| ALT > AST (ratio < 1) | Fatty liver (NAFLD), viral hepatitis, medication effect |
| AST/ALT ratio > 2:1 | Alcoholic liver disease (especially with elevated GGT) |
| AST elevated, ALT normal | Muscle source — check CK (creatine kinase); consider recent exercise or cardiac event |
| Both massively elevated (> 1000 U/L) | Acute liver injury — ischaemia, acetaminophen overdose, acute viral hepatitis. Urgent care. |
Clinical Pearl
AST > ALT with ratio > 2:1 is the classic pattern for alcoholic liver disease. In contrast, fatty liver (NAFLD) almost always shows ALT > AST. If your AST is elevated but ALT is normal, the source is likely muscle — check whether you exercised hard before the draw.
What to Do With a Mildly Elevated Result
A single mildly elevated result (say, ALT of 50–80 U/L) is not a reason to panic. The most important next step is a repeat test 4–8 weeks later — without heavy exercise, alcohol, or new medications in the period beforehand. Transient elevations are common and often resolve on their own.
If the elevation persists on repeat testing, the workup typically includes:
When to Seek Urgent Care
If ALT or AST is above 400 U/L, you experience jaundice (yellowing skin/eyes), right upper abdominal pain, or dark urine — seek same-day medical evaluation. These can indicate acute liver injury.
Lifestyle Changes That Lower Liver Enzymes
For NAFLD — by far the most common cause — liver enzymes are highly modifiable through lifestyle:
See your full liver panel score
Upload your blood test PDF and get an instant A–F liver domain score across ALT, AST, ALP, albumin, bilirubin, and GGT.
Analyze My Blood Test →Emergency note: If you are experiencing symptoms of a medical emergency, call emergency services (911 in the US / 999 in the UK / 112 in the EU) immediately. Do not rely on this website in an emergency situation.
Medical Disclaimer
This article is for educational purposes only and does not constitute medical advice. Reference ranges, supplement dosages, and nutritional information mentioned are general educational guidance from published research—not personalised recommendations. Do not use this content to self-diagnose or self-treat any condition. Always consult a qualified healthcare provider before making any changes to your health regimen, medications, or supplements.
See exactly where your results stand
Upload your blood test PDF and get a free A–F score across all 6 health domains in seconds.
Analyze My Blood Test →