The ALT (alanine aminotransferase, also called alanine transaminase) blood test measures the level of the enzyme ALT in your blood. ALT is an enzyme — a protein that helps speed up chemical reactions in the body — found mainly in the liver, and when liver cells are damaged they release ALT into the bloodstream, so the blood level is used as a general marker of liver health.
ALT is commonly measured to help check the health of your liver and to help diagnose or monitor liver injury or disease. It is often part of a routine blood screening and is usually done alongside other liver tests (such as AST, ALP, and bilirubin) rather than interpreted on its own.
MedlinePlus's Medical Encyclopedia gives a general normal range of about 4 to 36 U/L (0.07 to 0.60 µkat/L). This is a general guide only: normal value ranges can vary slightly among different labs, and some labs use different measurements or test different samples, and results can also be influenced by factors such as age, sex, and method. Because of this, the reference range printed on your own lab report is the one that applies to your result — a single number should not be read as a personal diagnosis.
A higher-than-usual ALT level may be a sign of liver injury or disease, and it is most meaningful when other liver test values are also raised. As general, hedged possibilities (not a diagnosis and not a complete list), higher levels can be seen with conditions such as hepatitis, infection, cirrhosis, fatty liver, liver tumors or liver cancer, reduced blood flow to the liver, hemochromatosis, mononucleosis, pancreatitis, and the effects of certain medicines or poisons (for example alcohol or acetaminophen). A high ALT does not always mean there is a medical condition that needs treatment.
Lower-than-usual ALT levels are not commonly reported and are generally not a focus of this test. MedlinePlus notes that, when seen, low levels may be associated with things such as vitamin B6 deficiency or chronic kidney disease. This is general information, hedged, and not a diagnosis. Your results are interpreted in the context of your overall health, symptoms, and other tests, and your health care provider is the right person to explain what your specific ALT result means for you. This is general information, not medical advice.
Reference ranges vary by laboratory, age, sex, and method — the range on your own report is what applies to you. A single value out of range doesn’t confirm any condition; your clinician interprets it alongside your symptoms, history, and other results. This page is general information, not medical advice.
General reference, not medical advice, and not a substitute for your clinician. Lab reference ranges and interpretation depend on the laboratory and on your individual situation — discuss your results with a licensed healthcare professional.