AST (aspartate aminotransferase) blood test: what it means
What it measures
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.
Why it’s ordered
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.
General reference range
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.
If it’s high
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.
If it’s low
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.
A result is not a diagnosis
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.
Medicines that can move this result
Acetaminophen overdose injures liver cells directly, which spill AST into the blood. The rise starts 24 to 72 hours after the ingestion and is extreme, often above 2000 U/L, with symptoms following a day or two later.
Source ↗Simvastatin causes mild, symptom-free aminotransferase rises — AST is one of them — that usually settle on their own. Separately, statins can inflame or break down muscle, and because damaged muscle also releases AST, a muscle problem can raise AST with no liver injury at all. A creatine kinase test tells the two apart.
Source ↗Atorvastatin produces mild, symptom-free rises in aminotransferases — AST and ALT — in 1% to 3% of people. They are usually temporary, and LiverTox notes most did not require any change of dose.
Source ↗On the long-term, low-to-moderate weekly doses used for arthritis and psoriasis, AST rises are frequent but usually mild. About 5% exceed twice the normal ceiling, and those levels fall quickly when the dose is paused or reduced — which is why blood tests are scheduled with this drug.
Source ↗When this antibiotic combination injures the liver, AST and ALT can both climb many times above normal — in the case LiverTox describes, 8 to 20 fold. The injury often begins after the course of tablets has already been finished, on average about three weeks after starting.
Source ↗A toxic by-product formed as the liver processes isoniazid damages liver cells, releasing AST and ALT. Most rises are symptom-free and often settle even on continued treatment; liver tests are recommended, usually monthly at first, for people at higher risk such as those with existing liver disease or over 50.
Source ↗Amiodarone is fat-soluble and accumulates in tissues including the liver during long-term use, and enzyme rises are reported in 15% to 50% of people on it, more often at higher daily doses. Scheduled AST and ALT checks are part of standard monitoring for this drug.
Source ↗Fluconazole can inflame the liver in the first weeks of use. In a Kaiser Permanente database of about 179,000 people treated with oral fluconazole, clearly raised AST or ALT above 200 U/L showed up in roughly one patient in eighty, and severe acute liver injury in one in five hundred.
Source ↗Do not stop a prescribed medicine over a lab number. These are recognised associations, not a finding about your result — your value may have nothing to do with any medicine you take, and the list is not complete. Bring it to whoever prescribed the drug; they can weigh it against why you are taking it.
Frequently asked
- What does the AST (aspartate aminotransferase) blood test measure?
- 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.
- What is a normal AST (aspartate aminotransferase) blood test range?
- 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.
- What does a high result mean?
- 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.
- What does a low result mean?
- 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.
Other lab tests
Sources
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.