The essentials

High liver enzymes, mainly ALT and AST (also called transaminases), mean liver cells are irritated or injured, or that AST is coming from muscle. A mild rise is common and often has a treatable cause such as fatty liver, a medicine, alcohol or hard exercise. A very high value, yellow skin or eyes, or severe abdominal pain needs care the same day. The pattern across several results, not one number, guides the next step.

What does a high ALT or AST mean on my lab report?

ALT is found mainly in the liver. AST is found mainly in the liver but also in the heart, muscles and other tissues[1][2]. When liver cells are damaged, they release these enzymes into the blood[1]. Here is a fictitious line from a report, in US format.

Fictitious example of a lab report line (United States format)
TestResultReference rangeFlag
ALT (alanine aminotransferase)74 U/L7-55 U/LH
AST (aspartate aminotransferase)52 U/L8-48 U/LH
Alkaline phosphatase (ALP)88 U/L40-129 U/L-
Total bilirubin0.8 mg/dL0.1-1.2 mg/dL-
  1. Result: the amount of enzyme activity in your blood, in units per liter.
  2. Reference range: set by your laboratory; yours may differ from this example.
  3. Flag H: above the range. ALT and AST high with ALP and bilirubin normal is called a hepatocellular pattern: ALT and AST rise out of proportion to alkaline phosphatase[3].

Have a report with H next to ALT or AST? BloodSense walks you through every line and helps you prepare questions for your doctor.

Get my liver tests explained

Many laboratories still use older upper limits. A large study of healthy blood donors proposed lower limits (30 U/L for men, 19 U/L for women, against 40 and 30)[5], and the American College of Gastroenterology says a true healthy ALT is 29 to 33 IU/L in men and 19 to 25 IU/L in women, and values above should be assessed[3]. A result just under your lab's limit is not always the end of the story.

When should I see a doctor about high liver enzymes?

Most people feel well, but liver disease can cause nausea, loss of appetite, fatigue, jaundice, abdominal pain or swelling, dark urine, pale stool and itching[1].

When to see a doctor

  • Emergency: call 911 for yellow skin or eyes with confusion or drowsiness, vomiting blood, black stool, severe abdominal pain, or after swallowing too much acetaminophen, even if you feel fine[8].
  • Within 24 to 48 hours if you notice jaundice, dark urine with pale stool, new abdominal swelling or intense itching[1].
  • At your next appointment if you feel well and the rise is mild. Bring the full list of your medicines and supplements.

What causes high liver enzymes?

  • Common Fatty liver. Experts estimate that about 24% of US adults have it[7]. It is now called metabolic dysfunction-associated steatotic liver disease (MASLD), and it is linked to excess weight, diabetes and abnormal blood fats[6][7]. ALT also tracks body mass index and lipid and sugar metabolism[5].
  • Common Medicines and supplements, including cholesterol and pain medications[1]. Acetaminophen over 4000 mg a day from all sources can damage the liver[8].
  • Common Alcohol. Toxic drug or alcohol use can raise AST and ALT[2].
  • Possible Viral hepatitis (A, B or C), checked in the standard work-up[3]. See hepatitis C and hepatitis B.
  • Possible Muscle or heart sources for AST, and intense exercise for both[1][2]. Infection such as mononucleosis, pancreatitis, burns and seizures are also listed[2].
  • Possible Inherited or immune diseases: hemochromatosis (iron overload), autoimmune hepatitis, Wilson's disease and alpha-1 antitrypsin deficiency[3].
  • Rare Cirrhosis or liver cancer, reduced blood flow to the liver[1]. See cirrhosis.

Can a high result be a false alarm?

Yes. A high result does not always mean you have a condition needing treatment: age, sex, weight, medicines, supplements, intense exercise and the menstrual cycle can all change it[1]. Tell the person who reads your results about a hard workout before the blood draw, new supplements or a change in medicines. Do not stop any medicine unless your provider says so[2].

What tests will the doctor order next?

How high the values are helps guide the evaluation[3], and UK guidelines also tie the next investigations to how far and how long they stay raised[4]. For a hepatocellular pattern, the work-up usually covers the following[3]:

  • A review of prescribed and over-the-counter medicines, plus alcohol use
  • Blood tests for hepatitis A, B and C
  • Assessment for fatty liver and alcohol-related liver disease
  • Screening for hemochromatosis, autoimmune hepatitis, Wilson's disease and alpha-1 antitrypsin deficiency
  • Imaging of the liver; a biopsy only if blood tests and imaging do not explain it

Other liver tests help sort the pattern: alkaline phosphatase and GGT for bile ducts, and bilirubin, which is split into direct and indirect parts when high[3]. For the enzymes themselves, see ALT and AST.

Questions to ask your doctor

  1. How far above the limit are my ALT and AST, and are my ALP and bilirubin normal?
  2. Could one of my medicines or supplements be the cause?
  3. Should the test be repeated, and when?
  4. Do I need a hepatitis test or a liver imaging exam?

Frequently asked questions

Can high liver enzymes go back to normal?

When the cause is a medicine, alcohol or a temporary factor such as hard exercise, values can change once it is removed. Your provider decides which cause applies[1].

Do I need to fast for a liver enzyme test?

ALT alone does not need it, but it is usually ordered with other tests that may. Follow your provider's instructions[1]. See fasting before a blood test.

Are ALT and AST the same as "liver function"?

No. They mainly show cell injury. Experts prefer the term liver chemistries or liver tests[3].

Can acetaminophen cause high liver enzymes?

Taking too much can cause liver damage; do not exceed 4000 mg a day from all sources[8].

References

  1. MedlinePlus Lab Tests. ALT blood test. medlineplus.gov (accessed October 22, 2026)
  2. MedlinePlus Lab Tests. AST test. medlineplus.gov (accessed October 22, 2026)
  3. Kwo PY, Cohen SM, Lim JK. ACG clinical guideline: evaluation of abnormal liver chemistries. Am J Gastroenterol. 2017;112(1):18-35. doi:10.1038/ajg.2016.517 (accessed October 22, 2026)
  4. Newsome PN, Cramb R, Davison SM, et al. Guidelines on the management of abnormal liver blood tests. Gut. 2018;67(1):6-19. doi:10.1136/gutjnl-2017-314924 (accessed October 22, 2026)
  5. Prati D, Taioli E, Zanella A, et al. Updated definitions of healthy ranges for serum alanine aminotransferase levels. Ann Intern Med. 2002;137(1):1-10. doi:10.7326/0003-4819-137-1-200207020-00006 (accessed October 22, 2026)
  6. Rinella ME, Lazarus JV, Ratziu V, et al. A multisociety Delphi consensus statement on new fatty liver disease nomenclature. J Hepatol. 2023;79(6):1542-56. doi:10.1016/j.jhep.2023.06.003 (accessed October 22, 2026)
  7. National Institute of Diabetes and Digestive and Kidney Diseases. Definition & facts of NAFLD & NASH. niddk.nih.gov (accessed October 22, 2026)
  8. MedlinePlus Drug Information. Acetaminophen. medlineplus.gov (accessed October 22, 2026)

This article is general health information. It does not replace a medical examination, diagnosis or treatment. If you have yellow skin or eyes, severe abdominal pain or confusion, seek care without waiting.