An aspartate aminotransferase test, also called an AST test, is a blood test. It's commonly used to check the health of the liver. AST is a substance found mostly in the liver. But it's also in the heart, kidneys, muscles and other organs. When tissues in these organs are damaged, AST can leak into the blood. So the AST level goes up.

An AST test isn't usually done by itself. It's commonly part of the following blood tests:

• Comprehensive metabolic panel.
• Liver panel or liver function tests.

AST is usually tested with another substance found in the liver called alanine aminotransferase, also known as ALT. Together, these two substances give a clearer picture of liver health.

Other names for an AST test are:

• Serum glutamic-oxaloacetic transaminase test.
• SGOT test.

An AST test is done to check for liver injury. It does not tell you how the liver is working.

Your healthcare professional may do this test as part of routine blood work to check your general health. Checking your AST level can help find liver changes early, even before you feel sick.

You may need an AST test if you have:

• Liver disease.
• Unexplained symptoms such as belly pain, yellowing of the skin or eyes, dark urine, or tiredness.
• Symptoms of liver disease during pregnancy.
• Long-term health conditions such as diabetes or obesity.
• Unexplained muscle pain or weakness.

Your healthcare professional also may do an AST test if you:

• Drink alcohol regularly.
• May have been exposed to a liver infection called hepatitis.
• Take supplements or medicines that affect the liver.

An AST test can help diagnose:

• Alcohol-related liver disease.
• Inflammation of the liver.
• Scarring of the liver, called cirrhosis.
• Viral hepatitis A, B or C.
• Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly called nonalcoholic fatty liver disease (NAFLD).
• Metabolic dysfunction-associated steatohepatitis (MASH), formerly called nonalcoholic steatohepatitis (NASH).

An AST test is not used to diagnose liver cancer or other cancers. But it may be done with other tests if your healthcare professional thinks cancer is possible.

An AST test is a blood test. For most people, an AST test is quick and easy, with no side effects. But possible risks of getting a blood test are:

• Soreness or tenderness in the area where the blood is taken.
• Bruising near the area where the blood is taken.
• Bleeding.
• Fainting or feeling lightheaded.
• Infection of the area where the blood is taken. This is rare.

These effects usually go away on their own. If you feel dizzy, tell the person taking your blood right away. You need to rest until you feel better.

Most people don't need to do anything special to get ready for an AST blood test. No special clothing is needed. But it might help to wear a short-sleeved shirt.

Here are a few things that might affect your test results.

• Medicines. Some medicines and supplements can raise AST levels. For example, very high doses of acetaminophen (Tylenol, others) can damage the liver, which makes AST levels go up. Tell your healthcare team about all the medicines and supplements you take. Include those bought without a prescription. Do not stop taking any medicines unless your healthcare team tells you to do so.
• Food and drinks. Eating a lot of fast food or sugar-sweetened drinks may raise your AST blood level. This is more common in people who are overweight and have diabetes. You may be told not to eat or drink for a while before an AST test, especially if you're having other blood work done. This is called fasting. Ask your healthcare team whether you need to stop eating or drinking for a short time before the test.
• Alcohol. Alcohol often can make your AST level go up. Do not drink alcohol for at least 24 hours before your test.
• Exercise. Your healthcare professional may tell you not to exercise before an AST test. Heavy exercise or weightlifting can raise your AST level. That's because AST also is found in your muscles, not just your liver. When muscles are used a lot or get sore, they can send AST into your blood.

Tell your healthcare team if you've had a recent illness or a muscle injury. These things also may affect results.

Before

Your healthcare team tells you where to go for your AST blood test. The test may be done in your healthcare professional's office, or in a clinic, hospital or lab.

Tell your healthcare professional if:

• You are anxious about needles.
• You've fainted during a blood test.
• You have a bleeding disorder.

During

To do the AST test, a healthcare professional takes a small sample of your blood.

You usually sit in a chair for the test. The healthcare professional places a small needle into one of your veins, usually in your arm. You might feel a small pinch or sting when the needle goes in.

A tube attached to the needle collects the blood and empties it into a small container. The container goes to a lab. When your test is done, your healthcare professional puts a small bandage on your arm.

After

You might have a small bruise or feel sore where the needle went in. That usually goes away in a day or two. Most people can go back to daily activities right away.

Your healthcare team gives you your AST test results. Most people get results in about 1 to 2 days. Test results help your healthcare team make a diagnosis and plan treatment, if needed.

Remember this when looking at your AST results:

• Mild changes in AST are common. They are not always a concern.
• A single AST number doesn't give enough information to make a diagnosis. Your healthcare professional considers your symptoms and results of other tests.
• AST liver levels can go up and down based on exercise and diet.

Results of an AST test are given in units per liter (U/L). AST levels vary depending on age and sex. But here are the general ranges:

• Males (14 years and older): 8 to 48 U/L.
• Females (14 years and older): 8 to 43 U/L.
• Children (1 to 13 years):
  • Boys: 8 to 60 U/L.
  • Girls: 8 to 50 U/L.

Different labs may use slightly different numbers for AST results. Ask your healthcare team what the target AST goal is for you.

Causes of low AST

AST levels that are below the standard range are not common. Some conditions or treatments that can cause low AST are:

• Too little vitamin B-6, also called B-6 deficiency.
• Chronic kidney disease, also called CKD.
• Kidney dialysis.
• Extreme liver failure.
• Too little of the nutrients the body needs to stay healthy, also called malnutrition.

Causes of high AST

Many times, a small increase in the AST level is not a concern. Heavy exercise or a fatty meal may cause your AST level to go up. Your healthcare professional looks at how high your number is and runs other tests to find the cause.

Liver-related causes of high AST include:

• Alcohol-related liver disease.
• Metabolic dysfunction-associated steatotic liver disease, also called MASLD.
• Metabolic dysfunction-associated steatohepatitis, also called MASH.
• Hepatitis.
• Liver irritation or damage from medicines or supplements.
• Scarring of the liver, called cirrhosis.

An AST test may be done during pregnancy to check liver health. Some pregnancy complications can cause high levels of AST. These conditions include:

• Preeclampsia, a condition marked by high blood pressure and signs of organ damage.
• HELLP syndrome, an extreme form of preeclampsia.
• Acute fatty liver of pregnancy, a rare but life-threatening liver disease. It happens in the last three months of pregnancy.
• Intrahepatic cholestasis of pregnancy, a condition that causes extreme itching. It happens because the liver can't remove a substance called bile.

Sometimes, an increase in AST is not related to the liver. That's because AST also is found in the heart, muscles and other organs. Other causes of high AST are:

• A type of extreme muscle tissue damage called rhabdomyolysis.
• Muscle injury from extreme exercise or diseases such as muscular dystrophy.
• Congestive heart failure.
• Heart attack.

Causes of dangerously high AST

An AST level is considered dangerously high if it is 15 times greater than the highest number in the standard range.

An AST level over 10,000 IU/L often means there is a life-threatening condition. Medical help is needed right away to find and treat the cause.

If your AST level is dangerously high, your healthcare professional looks for serious causes such as:

• Acetaminophen overdose.
• Severe hepatitis or liver inflammation.
• Very low blood flow to the liver, called shock liver.

If your AST results are too high or too low, your healthcare team may:

• Do the test again in a few weeks or months.
• Order other blood tests or imaging tests.
• Ask about your diet and exercise habits to see if they could be a cause.
• Talk with you about the medicines you take and how much alcohol you drink.
• Send you to a liver specialist, if needed.

Many causes of high or low AST are treatable or manageable. Talk with your healthcare professional about your results and the next steps.