Lab test
What is an ALT blood test, and what is a normal ALT level?
An ALT blood test measures alanine aminotransferase, an enzyme found mainly in the liver that leaks into the blood when liver cells are damaged. It is part of routine liver checks and the CMP. The American College of Gastroenterology defines a healthy ALT as 29 to 33 IU/L for men and 19 to 25 IU/L for women.
What does the ALT test measure?
ALT is an enzyme found mainly in the liver. When liver cells are damaged they release ALT into the blood, so high levels may be a sign of liver injury or disease. MedlinePlus
Because ALT is mostly found in the liver, it checks more specifically for liver damage than AST. MedlinePlus
Why is the ALT test ordered?
- As part of a routine checkup or a liver function panel, often within a CMP. MedlinePlus
- For symptoms of liver damage such as jaundice, dark urine, abdominal swelling, nausea or itching, or for higher risk because of alcohol use, obesity, diabetes or certain medicines. MedlinePlus
What are typical ALT ranges?
ARUP Laboratories reports its ALT interval "by report", because it varies by instrument. The ACG guideline sets a healthy range. ARUP Laboratories
Reference ranges differ between laboratories and testing methods, and many also differ by age, sex, pregnancy or the phase of the menstrual cycle. The range printed on your own report is the one that applies to your result, and a clinician interprets it alongside your history.
| Group | Healthy ALT |
|---|---|
| Men | 29 to 33 IU/L |
| Women | 19 to 25 IU/L |
The ACG guideline grades elevations by multiples of the lab’s upper limit of normal: under 2 times is borderline, 2 to 5 times mild and 5 to 15 times moderate, with a separate evaluation above 15 times. ACG Clinical Guideline
What can affect ALT results?
- Some medicines can affect the result; you may also be asked to fast if ALT is drawn with other tests. MedlinePlus
- The amount of ALT in the blood is not related to how much the liver may be damaged. MedlinePlus
When should you talk to a clinician about a ALT result?
- Your provider compares ALT with other liver tests before deciding whether more tests are needed; the ACG guideline says levels above its healthy range should be assessed by a physician. ACG Clinical Guideline
DiscoverMedica explains what a test measures and what named sources publish. It does not interpret individual results; the clinician who ordered your test, or one you choose, does.
Where can you get a ALT test?
A clinician can order it as part of routine or follow-up care. Some services also let you order lab tests yourself; check that a service’s panel includes this marker, which laboratory runs it, and who reviews the result with you.
- Function HealthAnnual membership for broad lab panels, drawn at Quest sites or at home.
- Quest HealthOrder individual lab tests from Quest Diagnostics online, without a doctor’s visit.
ALT Blood Test: questions, answered
What is a normal ALT level?
The American College of Gastroenterology guideline defines a healthy ALT as 29 to 33 IU/L for men and 19 to 25 IU/L for women, lower than some lab ranges. ARUP Laboratories reports its range by instrument. Compare a result with your report and ask the clinician who ordered it. The guideline says levels above its healthy range should be assessed by a physician.
What causes high ALT?
MedlinePlus lists hepatitis, infection, cirrhosis, liver cancer and other liver diseases. The ACG guideline also lists fatty liver disease, alcohol, hemochromatosis and drug or supplement related injury among the causes a clinician looks for. MedlinePlus notes that the amount of ALT does not show how much damage there is.
What is the difference between ALT and AST?
Both are enzymes released when cells are damaged. ALT is found mainly in the liver, so it is more specific for liver damage; AST is also found in the heart, muscles and other tissues. They are usually measured together. Ask the clinician who ordered them.
Sources
- MedlinePlus: ALT Blood Test
- ARUP Laboratories: Alanine Aminotransferase (test 0020008)
- ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries (Am J Gastroenterol 2017)
Last reviewed October 7, 2026. Every source above was checked on or before that date. Educational information only, not medical advice; it does not replace a conversation with a licensed clinician. DiscoverMedica does not employ clinicians.