The AST (aspartate aminotransferase) blood test measures the amount of AST in your blood. AST is an enzyme (a protein that helps speed up chemical reactions in the body), found mainly in the liver but also in the heart, muscles, and other tissues. When cells in these tissues, especially the liver, are injured, AST can be released into the bloodstream, so the level offers a clue about liver health.
An AST test is often part of routine blood screening to check liver health and is commonly done together with other tests (such as ALT, ALP, and bilirubin) to help diagnose or monitor liver disease. A clinician may order it during a checkup, to look into signs that could point to a liver problem (for example nausea, fatigue, jaundice, abdominal swelling, or dark-colored urine), or to monitor a known liver condition; AST is only one piece of the picture and is interpreted alongside these other tests.
As a general reference, MedlinePlus lists a normal range of about 8 to 33 U/L (0.13 to 0.55 µkat/L). This is only a general guide. Normal value ranges may vary slightly among different laboratories, and results can also be affected by factors such as age, sex, pregnancy, exercise, and certain medicines; different labs may use different methods, samples, or units. Because of this, the reference range printed on your own lab report, next to your result, is the one that applies to you. A number by itself is not a diagnosis.
A higher-than-usual AST level is a general signal that some tissue, often the liver, may be releasing the enzyme, but it does not identify a specific cause on its own. An increased AST can be seen with a range of conditions and situations, and the following is not a complete list. It may be associated with liver-related problems such as hepatitis, cirrhosis, death of liver tissue, reduced blood flow to the liver (liver ischemia), liver cancer or tumor, and effects of alcohol or certain medicines (such as acetaminophen). Because AST is also present in the heart and muscles, higher levels can also be seen with conditions such as a heart attack, muscle disease or injury, pancreatitis, hemochromatosis, or mononucleosis, and after events like burns, seizures, surgery, or heart procedures. Pregnancy and exercise may also raise AST. Only a clinician can determine what an elevated result means for a particular person, using the full clinical picture and other tests.
Low levels of AST in the blood are usually considered normal. AST is generally not interpreted as being abnormally "low," so a low or low-normal result is typically not a cause for concern on its own.
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.