Alt
An ALT test measures the level of alanine aminotransferase enzyme in your blood to evaluate liver function.
{"ALT is a liver enzyme that helps convert food into energy","Elevated ALT levels may indicate liver damage or disease","The test is performed on a blood sample taken from a vein","Normal ALT levels vary by age, sex, and laboratory","Certain medications and conditions can affect ALT results"}
Key facts at a glance
- LOINC
- 1742-6
- Short code
- ALT
- Synonyms
- —
- Category
- liver
- Sample
- serum
- Container
- Serum Separator Tube (SST) or Red Top Tube
- Units
- U/L
- Ref low
- 7
- Ref high
- 56
- Critical range
- 5 U/L – 900 U/L
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–120 years
- Method
- enzymatic-colorimetric
- CPT
- 84460
- SNOMED
- 389067008
- Specimen volume
- 1 mL minimum, 3.5 mL preferred
- Stability
- Room temperature: 24 hours, Refrigerated (2-8°C): 7 days, Frozen (-20°C or below): 30 days
- Hemolysis max
- 50
- Lipemia max
- 300
- Icterus max
- 20
- TAT
- 1–4 hours
What is an ALT Test?
The ALT (alanine aminotransferase) test is a blood test that measures the amount of this enzyme in your blood. ALT is primarily found in the liver, but smaller amounts are also present in the kidneys, heart, and muscles. When liver cells are damaged or destroyed, ALT is released into the bloodstream, causing elevated levels.
Why is it Performed?
An ALT test is commonly ordered as part of a routine liver function panel or metabolic panel. It helps healthcare providers assess liver health, diagnose liver conditions such as hepatitis or fatty liver disease, monitor the effects of certain medications on the liver, and evaluate symptoms like jaundice, abdominal pain, or unexplained fatigue.
How is the Test Done?
A healthcare professional will draw a small blood sample from a vein in your arm using a needle. The sample is then sent to a laboratory for analysis. The procedure is quick and generally causes minimal discomfort. You may experience slight bruising or soreness at the injection site.
How to Prepare for the Test
No special preparation is usually required for an ALT test. However, your doctor may ask you to fast for 8-12 hours before the test if other blood tests are being performed simultaneously. Inform your healthcare provider about all medications, supplements, and herbal products you are taking, as some substances can affect test results.
Reference range
Adult males: 7-56 U/L; Adult females: 7-43 U/L. Pediatric reference ranges vary by age and laboratory. Some labs use a single reference range of 10-40 U/L.U/L
No fasting required. Avoid strenuous exercise 24 hours prior to sample collection. Inform physician of any medications including over-the-counter drugs, herbal supplements, and alcohol use.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings3
Short name
ALT
Part of panels
Frequently asked questions
What are normal ALT levels?
Does a high ALT mean I have liver cancer?
How long does it take to get results?
Can I lower my ALT levels naturally?
Is the ALT test dangerous?
Sources
- 1Mayo Clinic - ALT TestSource
- 2
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 10, 2026. · Read our editorial policy