What is the normal range for AST and ALT?

Typical adult reference ranges are AST about 8–48 U/L and ALT about 7–55 U/L, but exact limits vary by laboratory, sex, age, body size, and assay method. Many hepatology guidelines consider lower ALT thresholds abnormal in healthy adults, especially above 29–33 U/L in men and above 19–25 U/L in women.

What does a high ALT level mean?

ALT is relatively liver-specific. Elevated ALT most often reflects hepatocellular injury from fatty liver disease, viral hepatitis, alcohol-associated liver disease, medication or supplement injury, autoimmune hepatitis, hemochromatosis, Wilson disease, or ischemic injury. Mild elevations are common and should be interpreted with symptoms, risk factors, bilirubin, ALP, INR, and repeat testing.

What does an AST/ALT ratio above 2 mean?

An AST/ALT ratio greater than 2 is classically associated with alcohol-associated liver disease, especially when GGT is also elevated. It can also be seen in advanced fibrosis or cirrhosis from other causes. The ratio is most useful when AST or ALT is actually elevated; it is less meaningful when both values are normal.

When are high AST or ALT levels urgent?

Urgent evaluation is appropriate for very high aminotransferases, especially levels above 1,000 U/L, or any elevation with jaundice, confusion, bleeding, severe abdominal pain, fever, hypotension, pregnancy, high INR, or suspected acetaminophen overdose. These patterns can reflect acute hepatitis, ischemic hepatitis, toxin injury, biliary obstruction, or acute liver failure.

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AST & ALT Levels — Normal Range & Meaning

Reference guide for aminotransferase liver enzymes, AST/ALT ratio interpretation, common causes of elevation, red flags, and related liver tests.

Quick Answer — Normal AST and ALT Range

AST: 8–48 U/L (0.13–0.80 µkat/L)

ALT: 7–55 U/L (0.12–0.92 µkat/L)

Ranges vary by laboratory. AST and ALT are best interpreted with alkaline phosphatase, bilirubin, albumin, INR, symptoms, medications, alcohol use, and risk factors for liver disease.

What Are AST and ALT?

AST (aspartate aminotransferase, formerly SGOT) and ALT (alanine aminotransferase, formerly SGPT) are intracellular enzymes released into the blood when hepatocytes or other tissues are injured.

ALT is more specific to the liver. AST is found in liver, heart, skeletal muscle, kidney, brain, and red blood cells, so an isolated AST elevation can come from muscle injury, hemolysis, myocardial injury, strenuous exercise, or liver disease.

Clinically, AST and ALT are markers of hepatocellular injury. They do not measure liver function by themselves. Synthetic function is better assessed with INR, albumin, and bilirubin, while cholestatic injury is suggested by alkaline phosphatase and GGT.

Normal AST and ALT Range

Test	Typical Adult Range	Main Tissue Sources	Clinical Notes
AST	8–48 U/L	Liver, skeletal muscle, heart, kidney, brain, red blood cells	Less liver-specific; check CK if muscle source is possible.
ALT	7–55 U/L	Primarily liver	More liver-specific; mild elevations are common in MASLD/fatty liver.

Many laboratories use ranges similar to Mayo Clinic and MedlinePlus references. The American College of Gastroenterology notes that a healthy normal ALT may be lower than many lab reference ranges: approximately 29–33 U/L for men and 19–25 U/L for women.

How High Is Mild, Moderate, or Severe?

Pattern	Approximate Level	Common Considerations
Mild elevation	<5× upper limit of normal	MASLD/fatty liver, alcohol, medications, viral hepatitis, hemochromatosis, celiac disease, thyroid disease, muscle injury.
Moderate elevation	5–15× upper limit of normal	Acute viral hepatitis, drug-induced liver injury, autoimmune hepatitis, biliary obstruction, ischemic injury in evolution.
Severe elevation	Often >1,000 U/L	Ischemic hepatitis, acetaminophen toxicity, acute viral hepatitis, severe drug-induced liver injury, acute biliary obstruction, acute liver failure.

Magnitude alone does not determine severity. A patient with only modest AST/ALT elevation can have advanced cirrhosis, while acute injury can cause dramatic enzyme elevations before synthetic function changes.

AST/ALT Ratio Meaning

The AST/ALT ratio, sometimes called the De Ritis ratio, compares AST to ALT. It is most helpful when at least one aminotransferase is elevated.

AST/ALT Ratio	Possible Meaning	Clinical Context
<1	ALT higher than AST	Common in MASLD/fatty liver, viral hepatitis, and many early hepatocellular injuries.
>1	AST higher than ALT	May be seen in advanced fibrosis/cirrhosis, alcohol-associated liver disease, muscle injury, or hemolysis.
>2	Classically associated with alcohol-associated liver disease	More supportive when GGT is elevated and AST/ALT are moderately elevated rather than extremely high.

Do not over-interpret the ratio when AST and ALT are both normal. A ratio above 1 with normal enzymes is usually not clinically meaningful by itself.

Common Causes of High AST and ALT

Hepatic Causes

Metabolic dysfunction-associated steatotic liver disease (MASLD/fatty liver) — common with diabetes, insulin resistance, obesity, dyslipidemia, and metabolic syndrome.
Alcohol-associated liver disease — AST often exceeds ALT; AST/ALT ratio may be >2, and GGT may be elevated.
Viral hepatitis — hepatitis A, B, C, E, EBV, CMV, and other infections depending on context.
Drug-induced liver injury — acetaminophen, antibiotics, antiepileptics, statins, supplements, bodybuilding products, and many other agents.
Autoimmune hepatitis — consider with positive ANA/ASMA, high IgG, or compatible clinical setting.
Hemochromatosis — iron overload; evaluate with transferrin saturation and ferritin when persistent.
Wilson disease — especially in younger patients or acute liver failure; evaluate with ceruloplasmin and copper studies when suspected.
Alpha-1 antitrypsin deficiency — can cause chronic liver disease and pulmonary emphysema.
Ischemic hepatitis — very high AST/ALT after hypotension, shock, severe heart failure, or hypoxemia.

Non-Hepatic Causes

Muscle injury or rhabdomyolysis — AST can be prominent; check creatine kinase (CK).
Strenuous exercise — can transiently elevate AST and ALT, especially AST.
Hemolysis — red blood cell breakdown can raise AST.
Thyroid disease — hypo- or hyperthyroidism can be associated with abnormal liver enzymes.
Celiac disease — can cause mild, persistent aminotransferase elevations.

When to Seek Urgent Care

AST or ALT abnormalities should be interpreted by a qualified clinician. Seek urgent medical evaluation if elevated liver enzymes occur with:

Jaundice, dark urine, pale stools, severe itching, or rapidly worsening symptoms.
Confusion, sleepiness, bleeding, easy bruising, or a high INR.
Severe right-upper-quadrant abdominal pain, fever, vomiting, or hypotension.
Known or possible acetaminophen overdose, toxic mushroom ingestion, or high-risk medication/supplement exposure.
Pregnancy, especially with abdominal pain, high blood pressure, headache, itching, or abnormal platelets.
Very high AST or ALT, particularly values above 1,000 U/L.

Related Tests & Calculators

AST and ALT become much more useful when interpreted with the rest of the liver panel and clinical context:

Alkaline phosphatase and GGT — help identify cholestatic or biliary patterns. See ALP Levels Reference.
Bilirubin — evaluates jaundice and excretory function. See Bilirubin Levels Reference.
Albumin and INR — markers of hepatic synthetic function.
Platelet count — low platelets can suggest portal hypertension or advanced fibrosis.
FIB-4 Index — FIB-4 Calculator uses age, AST, ALT, and platelets to estimate liver fibrosis risk.
MELD Score — MELD Calculator estimates liver disease severity using bilirubin, INR, creatinine, and sodium.
Child-Pugh Score — Child-Pugh Calculator classifies cirrhosis severity.

About This Test

Clinical Pearls

Key Points for Clinicians

Confirm abnormal liver chemistries with repeat testing unless the clinical presentation is urgent.
The R-ratio can classify liver injury pattern: R = (ALT ÷ ALT ULN) ÷ (ALP ÷ ALP ULN). R >5 suggests hepatocellular injury, R <2 cholestatic injury, and R 2–5 mixed injury.
AST is less liver-specific than ALT. If AST is isolated or disproportionate, consider CK, hemolysis markers, recent exercise, myocardial injury, and medication exposures.
Normal AST and ALT do not exclude advanced chronic liver disease, especially in established cirrhosis.
A careful medication, supplement, alcohol, viral hepatitis, metabolic, and family history is often more useful than a single enzyme value.

Specimen and Assay Notes

AST and ALT are measured from serum or plasma. Hemolysis can falsely increase AST because red blood cells contain AST. Values may vary by laboratory method, specimen handling, exercise, body composition, sex, and age. Always compare results with the reference interval reported by the performing laboratory.

References

Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries. Am J Gastroenterol. 2017;112(1):18-35.
American Association for the Study of Liver Diseases. How to approach elevated liver enzymes. AASLD Liver Fellow Network. Published 2025.
Mayo Clinic. Liver function tests. Standard ranges for ALT and AST. Accessed May 2026.
MedlinePlus Medical Encyclopedia. Aspartate aminotransferase (AST) blood test. U.S. National Library of Medicine.
Pratt DS, Kaplan MM. Evaluation of abnormal liver-enzyme results in asymptomatic patients. N Engl J Med. 2000;342(17):1266-1271.
Giannini EG, Testa R, Savarino V. Liver enzyme alteration: a guide for clinicians. CMAJ. 2005;172(3):367-379.

References last verified: May 2026