Aspartate Aminotransferase (AST) Test Decoded

Written by Deanna Altomara, Nancy LeBrun
Medically Reviewed by Melinda Ratini, MS, DO on April 27, 2025
8 min read

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 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.

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 usually does 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.

“AST in isolation is not as helpful as looking at the ALT as well, which is a little more liver-specific,” says Meena Bansal, MD, a gastroenterologist at the Mount Sinai Health System in New York. “The ratio between those two gives you a little more information about the potential severity of the liver disease."

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. But higher-than-normal AST levels could signal problems in your liver or other organs that produce AST.

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 may also do a fibrosis (scarring) assessment called FIB4. It uses the AST, ALT, platelet count, and age. The score that results from this assessment can tell your doctor if you need further testing for liver disease.  

Your doctor also might suggest this test if you have symptoms of liver damage, such as:

  • Yellow skin or eyes, called jaundice
  • Tiredness
  • Weakness
  • Swollen belly
  • Nausea
  • Vomiting
  • Stomach pain
  • Appetite loss
  • Itchy skin
  • Dark-colored urine
  • Light-colored poop
  • Swelling in your legs and ankles
  • Skin that bruises easily

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 metabolic dysfunction-associated steatotic liver disease (MASLD) (formely known as nonalcoholic fatty liver disease (NAFLD)

If you already have liver disease, your doctor might use this test to monitor your condition or see if your treatment is working.

If you have any of the liver diseases below, your doctor might use AST levels to watch over how they progress and plan treatment. These liver diseases include:

  • Hepatitis C
  • Hepatitis B
  • MASLD (formerly NAFLD), or metabolic dysfunction-associated steatotic liver disease. Steatotic means there is excess fat in the liver.
  • MASH (formerly NASH), or metabolic dysfunction-associated steatohepatitis
  • ALD, alcohol-associated liver disease (formerly known as alcoholic liver disease)
  • Cirrhosis
  • Liver cancer 

If your doctor says you need to have an AST blood test, that means you'll need to have some blood taken.

How can you prepare for an AST test?

You don't need any special preparation for the ALT test. But 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 blood tests.

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 taken, 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 taken, but you could have minor problems, such as:

  • A quick pinch when the needle is inserted
  • Problems locating a vein
  • Bleeding or bruising from the needle
  • Fainting or feeling dizzy for a few minutes after the test
  • Infection at the site where your skin was broken

Usually, you’ll get your results back in one to two business days. They're given in units per liter (units/L).

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.

Normal AST

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.

High AST

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)
  • ALD
  • MASLD
  • MASH
  • 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
  • Pregnancy
  • Pancreatitis
  • Hypothyroidism
  • 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

Low AST levels are usually what your doctor wants to see in your test. 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)

Certain factors can affect AST test results and elevate them when liver disease may not be present. 

According to Bansal, “Exercise can affect results because the AST enzyme can come from the muscle as well. If you have any kind of breakdown of red blood cells, that can increase the levels of AST. If you’re really dehydrated, you can have elevated levels.”

Other things that may affect AST test results include:

  • Age
  • Sex
  • Race
  • Diet and weight
  • Certain medications 
  • Pregnancy

You may be able to lower your AST level by working with your doctor to understand and address what's making it high. Here are some steps you can take:

  • Lose weight if you are overweight or have obesity. 
  • Stop or reduce excessive alcohol use.
  • Eat a healthy diet to manage cholesterol and blood sugar levels.
  • Exercise regularly.

Unless you have advanced liver disease such as cirrhosis, your liver has a remarkable ability to heal. 

“Liver disease can pretty much be reversed,” says Bansal. “If you have scarring of the liver, and you address what’s causing the scarring, you can see reversal of fibrosis if you catch it early enough and you take away what’s causing the injury.”

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)
  • Bilirubin
  • 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.

  • The AST test is one of several simple tests your doctor can use to check you for possible liver disease. AST is an enzyme made by the liver. 
  • If your test shows you have high levels of the AST enzyme, you may have liver disease, but you'll need further testing to be sure. Some people who are healthy may also have a high AST level.
  • You may be able to work with your doctor to lower your AST levels if the underlying cause is obesity, excessive alcohol use, or high cholesterol. 
  • The liver has the ability to heal itself in some instances if you address the cause of the damage. It can often reverse the scarring that is the main sign of liver disease.

What is an AST blood test? 

AST stands for “aspartate aminotransferase,” an enzyme found in several organs, including the liver. An AST blood test is part of a diagnostic process to find out if you have potential liver disease.

What should I to do if my AST is high?

If your AST level is high, talk to your doctor so that you understand why. You can address some causes of an elevated AST, including obesity, excessive alcohol use, and high cholesterol.

What AST levels indicate fatty liver?

AST test results are given in units per liter. A level over 40 units per liter can mean a fatty liver or other liver disease, though it is not conclusive. Your doctor will order further tests to determine if a fatty liver is elevating your AST.

What level of AST is dangerous?

An AST level of greater than 500 units per liter is very high. It can be a sign of acute hepatitis, serious liver damage, liver cancer, or “shock liver” from lack of blood flow or oxygen.