The aspartate aminotransferase (AST) test is a blood test that checks for liver damage. Your doctor might order this test to find out if you have liver disease and to monitor your treatment.
Your liver is an organ that has many important jobs.
It makes a fluid called bile that helps your body digest food. It also removes waste products and other toxins from your blood. It produces proteins, as well as substances that help your blood clot. Alcohol or drug use and diseases such as hepatitis can damage your liver and keep it from doing these jobs.
AST is an enzyme your liver makes. Other organs, like your heart, kidneys, brain, and muscles, also make smaller amounts. AST is also called SGOT (serum glutamic-oxaloacetic transaminase).
Normally, AST levels in your blood are low. When your liver is damaged, it puts more AST into your blood, and your levels rise.
A high AST level is a sign of liver damage, but it can also mean you have damage to another organ that makes it, like your heart or kidneys. That's why doctors often do the AST test together with tests of other liver enzymes.
Why Would I Need This Test?
Your doctor can order an AST test if you have symptoms of liver damage, such as:
- Yellow skin or eyes, called jaundice
- Swollen belly
- Stomach pain
- Appetite loss
- Itchy skin
- Dark-colored urine
- Light-colored poop
- Swelling in your legs and ankles
Other reasons to have this test:
- You've been exposed to the hepatitis virus.
- You drink a lot of alcohol.
- You take medicine that's known to damage the liver.
- You have a family history of liver disease.
- You have obesity.
- You have diabetes or metabolic syndrome.
- You’ve had nonalcoholic fatty liver disease.
Your doctor might also want you to get this test to see if treatments you take for liver disease are working.
The AST test is also part of a comprehensive metabolic panel -- a blood test your doctor does as part of a routine exam.
How Do I Prepare?
You don't need any special preparation for the ALT test.
Tell your doctor what drugs or supplements you take. Some medicines can affect the results of this test.
What Happens During the Test?
A nurse or lab tech will take a sample of your blood -- usually from a vein in your arm. They will first tie a band around the upper part of your arm to make your vein fill with blood and swell up. Then they will clean an area on your arm with an antiseptic and put a needle in one of your veins. Your blood will go into a vial or tube.
The blood test should only take a couple of minutes. After your blood is drawn, the lab tech will take off the band and pull out the needle. They’ll put a piece of gauze and a bandage where the needle went in to stop the bleeding.
What Are the Risks?
The AST blood test is safe. Risks are usually minor, and can include:
- Pain when the needle is inserted
- Fainting or feeling dizzy
What Do the Results Mean?
You should have the results in about a day. They are given in units per liter (units/L). Normal ranges are:
- Males: 10 to 40 units/L
- Females: 9 to 32 units/L
Your exact range may depend on which lab your doctor uses. Talk with them about the specifics of your case.
Higher-than-normal AST levels can be caused by:
- Chronic (ongoing) hepatitis
- Cirrhosis (long-term damage and scarring of the liver)
- Blockage in the bile ducts that carry digestive fluid from the liver to the gallbladder and intestine
- Liver cancer
Very high AST levels can be caused by:
- Acute viral hepatitis
- Damage to the liver from drugs or other toxic substances
- A blockage in blood flow to the liver
Your doctor might also compare your AST and ALT levels. If you have liver disease, usually your ALT level will be higher than your AST level.
These other conditions not tied to your liver can also raise your AST level:
- Heart attack
- Intense exercise
- Muscle injury
Some diseases or medicines you take can cause a “false positive” result on the AST test. This means your test is positive, even though you don't have liver damage. Any of these can cause a false positive result:
- Diabetic ketoacidosis (Your body can’t make enough insulin, which helps sugar enter your cells.)
- Some antibiotics, such as erythromycin estolate or para-aminosalicylic acid (Paser)
Will I Take Other Tests?
AST is usually done as part of a group of liver function tests called a liver panel. It's often ordered with a test for alanine aminotransferase (ALT), another liver enzyme.
ALT is more accurate than AST at detecting liver disease. It can more accurately show whether the problem is in your liver or in another part of your body, like your heart or muscles.
Your doctor can compare the amount of ALT to AST in your blood to find out whether you have liver damage or a problem with another organ, such as your heart.
Your doctor might also do other tests of enzymes and proteins your liver makes, such as:
- Alkaline phosphatase (ALP)
- Total protein
Talk with your doctor to make sure you understand all of your liver test results. Also find out how these results might affect your treatment.