QUICK ANSWER
AST (aspartate aminotransferase) is an enzyme found primarily in the liver, skeletal muscle, cardiac muscle, and kidneys. When these cells are injured, AST leaks into the bloodstream, raising blood levels.
Normal range: 10–40 U/L (both sexes, LabCorp and Quest). Some labs use 10–35 U/L for women.
- High AST = cell injury — most commonly liver damage, but also muscle injury, heart damage, or intense exercise
- Low AST = generally not clinically significant; rarely indicates vitamin B6 deficiency or kidney disease
AST is almost always interpreted alongside ALT. The AST/ALT ratio narrows down the cause of liver enzyme elevation more precisely than either marker alone.
Key takeaway: A mildly elevated AST does not automatically mean liver disease. The ratio of AST to ALT, the degree of elevation, and the clinical context together determine the significance.
WHAT IS THE AST/ALT RATIO AND HOW DO YOU CALCULATE IT?
The AST/ALT ratio (also called the De Ritis ratio) compares the level of AST to ALT in the blood. It is one of the most clinically useful calculations in liver function assessment.
Formula: AST ÷ ALT = AST/ALT ratio
Example: If AST = 60 U/L and ALT = 40 U/L, the ratio is 60 ÷ 40 = 1.5
Worked examples:
| AST (U/L) | ALT (U/L) | Ratio | Interpretation |
|---|---|---|---|
| 60 | 40 | 1.5 | Mildly elevated ratio — evaluate in clinical context |
| 80 | 120 | 0.67 | ALT-predominant pattern — typical of NAFLD or viral hepatitis |
| 120 | 50 | 2.4 | Strongly suggestive of alcoholic liver disease when clinically appropriate |
To calculate your own ratio: divide your AST result by your ALT result. Both values should appear on the same lab report. If either value is within the normal range, see the section below on whether the ratio matters when levels are normal.
Normal AST/ALT ratio: In healthy individuals, the AST/ALT ratio is typically between about 0.8 and 1.3, though interpretation depends primarily on whether AST and ALT themselves are elevated above the upper limit of normal — not on the ratio alone. A ratio above 2 with elevated enzymes is a strong signal for alcoholic liver disease.
AST/ALT RATIO INTERPRETATION TABLE
| AST/ALT ratio | Most likely interpretation |
|---|---|
| Under 0.8 | Ratio in normal range — ALT-dominant pattern, common in NAFLD and viral hepatitis |
| 0.8–1.0 | Normal ratio |
| 1.0–1.5 | Mildly elevated ratio — may be normal or early liver disease; context-dependent |
| 1.5–2.0 | Moderately elevated — possible alcoholic liver disease, cirrhosis, or cardiac involvement |
| Above 2.0 | Strong indicator of alcoholic liver disease (De Ritis ratio) or cirrhosis |
| Above 3.0 | High specificity for alcoholic hepatitis; also seen in severe cirrhosis |
Important: The ratio is only meaningful when both AST and ALT are elevated above the upper limit of normal. If both are within the normal range, the ratio has no clinical significance regardless of the calculated value.
Specific ratio number lookup — what common values typically mean:
| AST/ALT ratio | Typical interpretation (when enzymes are elevated) |
|---|---|
| 0.5–0.7 | ALT-predominant pattern — common in NAFLD, viral hepatitis, medication-induced injury |
| 0.8–1.0 | Normal range — typical in healthy individuals |
| 1.0–1.2 | Often normal; mild ratio elevation; significance depends on actual AST and ALT levels |
| 1.2–1.5 | Mildly elevated ratio — evaluate in clinical context; possible early alcoholic liver involvement or cirrhosis |
| 1.5–2.0 | Moderately elevated — possible alcoholic liver disease, cirrhosis, or cardiac involvement |
| 2.0–3.0 | Strongly suggestive of alcoholic liver disease (when enzymes are elevated) |
| Above 3.0 | High specificity for alcoholic hepatitis or advanced alcoholic cirrhosis |
DOES THE AST/ALT RATIO MATTER IF LEVELS ARE NORMAL?
No — the AST/ALT ratio is clinically meaningless when both values are within the normal range.
If your AST is 22 U/L and your ALT is 18 U/L, the ratio is 1.22 — but since both values are normal, this ratio carries no diagnostic weight. The ratio is a tool for differentiating causes of liver injury, and liver injury requires elevated enzymes.
A ratio calculated from normal-range values should not be used to infer liver disease, alcoholic liver disease, or any other pathology. If your labs are normal, the ratio is not a concern.
WHAT IS THE DE RITIS RATIO?
The De Ritis ratio is simply another name for the AST/ALT ratio, named after Italian physician Fernando De Ritis who first described its clinical utility in the 1950s.
The key De Ritis ratio thresholds:
- < 1: More typical of non-alcoholic liver disease (viral hepatitis, NAFLD, medication-induced injury) — ALT tends to be more elevated than AST in hepatocellular disease
- > 2: Classic indicator of alcoholic liver disease — alcohol preferentially induces AST release and also depletes vitamin B6, which reduces ALT synthesis
- > 3: High specificity for alcoholic hepatitis or advanced alcoholic cirrhosis
Today the De Ritis ratio is used primarily to help differentiate causes of liver enzyme elevation — distinguishing alcoholic from non-alcoholic liver injury when both AST and ALT are elevated.
WHAT DOES HIGH AST MEAN?
High AST means cells containing this enzyme — most commonly liver, muscle, or cardiac cells — have been damaged and are releasing the enzyme into the bloodstream.
The degree of elevation provides context:
| AST level (U/L) | Elevation category | Common causes |
|---|---|---|
| 40–100 | Mildly elevated | NAFLD, strenuous exercise, medication effect, mild hepatitis |
| 100–300 | Moderately elevated | Alcoholic hepatitis, viral hepatitis, muscle injury, cholestasis |
| 300–1,000 | Markedly elevated | Acute viral hepatitis, alcoholic hepatitis, ischemic hepatitis, toxin exposure |
| Above 1,000 | Severely elevated | Acute viral hepatitis, ischemic hepatitis (shock liver), acetaminophen toxicity, rhabdomyolysis |
Common causes of high AST:
Liver causes
- Non-alcoholic fatty liver disease (NAFLD/NASH) — the most common cause of mild-moderate elevation in the US; typically AST/ALT ratio < 1
- Alcoholic liver disease — AST/ALT ratio typically > 2; rarely > 8 (severe ratios > 8 suggest non-alcoholic cause or mixed)
- Viral hepatitis (A, B, C) — can elevate AST to 1,000–10,000 U/L in acute infection; ALT typically higher than AST
- Cirrhosis — end-stage liver scarring; AST/ALT ratio often > 1 as regenerative capacity falls
- Drug-induced liver injury — statins, acetaminophen overdose, antibiotics, antifungals, antiepileptics
- Autoimmune hepatitis
- Hemochromatosis, Wilson's disease (metabolic liver diseases)
Muscle causes
- Rhabdomyolysis — severe muscle breakdown; AST may rise to thousands; check CK
- Myopathy or myositis — inflammatory muscle disease
- Strenuous exercise — transient AST elevation, normalizes within 24–72 hours
- Physical trauma, surgery, injections — local muscle injury
Cardiac causes
- Myocardial infarction (heart attack) — AST rises 6–10 hours after MI; largely replaced by troponin in modern cardiology
- Myocarditis — cardiac muscle inflammation
Other causes
- Thyroid disease — hypothyroidism associated with elevated CK and mildly elevated AST
- Hemolysis — red blood cell destruction releases AST (artifact, not true tissue injury)
- Celiac disease — unexplained liver enzyme elevation resolves on gluten-free diet
WHAT DOES LOW AST MEAN?
Low AST (typically below 10 U/L) is rarely clinically significant. Most of the time it is a normal variant or reflects normal physiological variation.
Causes of genuinely low AST:
- Vitamin B6 (pyridoxine) deficiency — AST enzyme activity requires vitamin B6 as a cofactor; deficiency reduces measured AST activity. This is the most well-established cause of low AST.
- Chronic kidney disease / uremia — uremic compounds may inhibit AST activity
- Pregnancy — AST may decrease in second and third trimester due to hemodilution
Low AST with normal ALT, ALP, GGT, and bilirubin requires no specific action in most cases. If other liver markers are abnormal alongside a low AST, vitamin B6 status should be considered.
AST VS ALT: KEY DIFFERENCES
| Feature | AST | ALT |
|---|---|---|
| Full name | Aspartate aminotransferase | Alanine aminotransferase |
| Primary location | Liver, muscle, heart, kidneys, RBCs | Liver (more liver-specific than AST) |
| Liver specificity | Lower — elevated in muscle and cardiac injury | Higher — mainly elevated in liver injury |
| Half-life | ~18 hours | ~48 hours |
| Pattern in NAFLD | Usually < ALT | Usually elevated, often higher than AST |
| Pattern in alcoholic liver disease | Usually > ALT (ratio > 2) | Lower relative to AST |
| Pattern in acute viral hepatitis | Both elevated; ALT typically higher | Both elevated; ALT typically higher |
ALT is more liver-specific than AST. When the question is "is this liver disease?", ALT is the more precise marker. When the question is "what type of liver disease?", the AST/ALT ratio helps differentiate.
WHEN TO FOLLOW UP
Discuss your AST result with a clinician if:
- AST is above 3× the upper limit of normal (> 120 U/L at most labs) without an obvious benign cause
- AST remains elevated on repeat testing 4–6 weeks after removing an obvious cause (alcohol, medication, exercise)
- AST is markedly elevated (> 300 U/L) — this warrants urgent evaluation
- AST is elevated alongside jaundice, abdominal pain, dark urine, or significant fatigue
- AST/ALT ratio is consistently above 2 with elevated enzymes — alcoholic liver disease workup warranted
- Low AST alongside other abnormal liver markers or suspected B6 deficiency
BOTTOM LINE
Bottom line: AST elevation tells you cells are injured; the AST/ALT ratio helps identify which cells and what cause. A ratio above 2 with elevated enzymes points strongly to alcoholic liver disease. A ratio below 1 is more typical of non-alcoholic liver injury. If both values are within the normal range, the ratio is clinically meaningless. Mildly elevated AST from exercise, alcohol, or medications is common and often resolves with removal of the trigger.
INTERNAL LINKS
Related liver function tests: ALT (Alanine Aminotransferase) · AST/ALT Ratio · ALP (Alkaline Phosphatase) · GGT · Bilirubin, Total · Albumin
Aspartate-aminotransferase (AST, SGOT)
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Frequently Asked Questions
Is ALT supposed to be higher than AST?
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