The aspartate aminotransferase (AST) test is a blood test that looks for liver damage by checking the levels of aspartate aminotransferase (also known as aspartate transferase) in your blood. Your doctor might order this test to find out if you have liver disease or to monitor your treatment if you currently have liver disease.
Other names for the AST test include:
- Serum glutamic-oxaloacetic transaminase test
- SGOT test
- Aspartate transaminase (AST) test
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.
What Is AST?
AST is an enzyme (a type of protein) made by your liver. Other organs, such as your heart, kidneys, brain, and muscles, also make smaller amounts of AST.
AST mostly stays in your liver, but it is normal to have small amounts of it in your blood. When your liver is damaged, more AST leaks into your blood. That's why high levels of AST in your blood are usually signs you could have liver damage. But it can also mean you have damage to another organ that makes AST, such as your heart or kidneys. That's why doctors often do the AST test together with tests of other liver enzymes.
AST vs. ALT
One test your doctor might do along with the AST test is the alanine transferase (ALT) test. ALT is also a type of enzyme, but unlike AST, it is found mostly in your liver. Your doctor might want to measure both of these because they can leak into your bloodstream when you have damage to certain cells.
If your results show high levels of ALT, it is almost a sure sign that you have some type of liver damage, likely from hepatitis, infection, cirrhosis, or cancer. However, higher-than-normal AST levels could signal problems in your liver or other organs that produce AST.
Why Would You Need an AST Test?
The AST test is part of the comprehensive metabolic panel, which is a routine blood test your doctor uses to monitor your overall health. It is often part of your regular checkups. Your doctor also might suggest this 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
Even if you don’t have these symptoms, your doctor might suggest this test if you're at a high risk for liver disease. Some risk factors include:
- Exposure to the hepatitis virus (e.g., you’ve injected drugs using shared needles)
- Drinking a lot of alcohol
- Taking medicine that's known to damage the liver
- Family history of liver disease
- Obesity, diabetes, or metabolic syndrome (conditions that increase your risk of heart disease)
- You’ve had nonalcoholic fatty liver disease
If you already have liver disease, your doctor might use this test to monitor your condition or see if your treatment is working.
AST Blood Test
If your doctor says you need to have an AST blood test, that means you'll need to have some blood drawn.
How can you prepare for an AST test?
You don't need any special preparation for the ALT test. However, if you're getting other tests (for example, as part of a comprehensive metabolic panel), you might need to fast for 10-12 hours beforehand. This means you can't eat or drink anything other than water. Ask your doctor if you need to fast before your bloodwork.
Also, tell your doctor what drugs or supplements you take. Some medicines can affect the results of this test.
What happens during an AST test?
A nurse or lab tech will take a sample of your blood, usually from a vein in your forearm. They'll first tie a band around the upper part of your arm to make your vein swell and fill with blood. Then they'll clean the area with an antiseptic and put a needle in your vein. Your blood will go into a vial or tube.
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 was to stop any bleeding. Then, they'll send the blood to a lab where it can be analyzed.
Risks of an AST test
The AST test is safe. There are few risks from having your blood drawn, but some people have issues, so you could have minor problems, such as:
- A quick pinch when the needle is inserted
- Problems locating a vein
- Bleeding or bruising at the place where the needle is injected
- Fainting or feeling dizzy for a few minutes after the test
- Infection at the site where your skin was broken
AST Test Results
Usually, you’ll get your results back in 1-2 business days. They're given in units per liter (units/L).
It’s important to remember that AST by itself doesn’t tell the whole story about your liver health. Your doctor gets a more accurate picture when they also consider your other test results, symptoms, and your medical history.
There’s no AST range that's normal for everyone. The numbers vary depending on the lab that tests your blood, and other factors including your age, weight, sex, and race. For example, 1 in 20 healthy people have abnormal levels of AST. But the most common range that is considered normal for an AST blood test is 8 to 33 units/L.
Talk to your doctor about your test to find out what they think is normal for you.
Higher-than-normal AST levels can be caused by:
- Chronic (ongoing) hepatitis
- Alcohol use
- Certain medications
- Cirrhosis (long-term damage and scarring of your liver)
- Blockage in the bile ducts that carry digestive fluid from your liver to your gallbladder and intestine
- Liver ischemia (lack of blood flow to your liver)
- Liver cancer
- Carbon tetrachloride (an industrial chemical used to make refrigerants and aerosols)
Very high AST levels (greater than 500 units/L) can be caused by:
- Acute viral hepatitis
- Large liver tumors
- Severe liver damage from drugs or toxins
- Shock liver (damage from lack of oxygen or blood flow)
Some other conditions not related to your liver can also raise your AST level:
- Hemochromatosis (when your body has too much iron)
- Mononucleosis (often called “mono”)
- Heart attack
- Muscle injury
- Certain central nervous system diseases
- Diabetic ketoacidosis (when your body can’t make enough insulin, which helps sugar enter your cells)
- Some antibiotics, such as erythromycin estolate or para-aminosalicylic acid (Paser)
Low AST levels are usually what your doctor wants to see in your test. However, high AST levels are a sign of concern. But there are cases when low AST levels can be caused by:
- Uremia (urinary waste in your blood)
- Vitamin B6 deficiency
- Some medications, including metronidazole (Flagyl) and trifluoperazine (Stelazine)
Liver Function Tests
The AST test is usually done as part of a group of liver function tests called a liver panel. This panel might include other enzymes and proteins made by your liver, such as:
- Alanine transaminase (ALT)
- Alkaline phosphatase (ALP)
- Total protein
If your results are abnormal, your doctor might recommend follow-up testing. These could include:
- Repeating the test(s)
- Different blood tests
- Imaging tests
- A liver biopsy
Talk with your doctor to make sure you understand all of your test results. Together, you can make a plan to start or adjust your treatment as necessary. This will help manage your health so that you can enjoy a better quality of life.