What is aspartate aminotransferase?

Aminotransferase (AST) is an enzyme that’s present in various tissues of your body. An enzyme is a protein that helps trigger chemical reactions that your body needs to function.

AST is found in the highest concentrations in your liver, muscles, heart, kidney, brain and red blood cells. A small amount of AST is typically in your bloodstream. Higher-than-normal amounts of this enzyme in your blood may be a sign of a health problem. Abnormal levels can be associated with liver injury.

AST levels increase when there’s damage to the tissues and cells where the enzyme is found. AST levels can rise as soon as six hours after damage to tissue occurs. The normal range for AST is higher from birth to age 3 compared to the normal ranges for older children and adults.

The AST test measures the amount of AST in your blood that has been released from injured tissue. An older name for the test is serum glutamic-oxaloacetic transaminase (SGOT).

Doctors commonly use the AST test to check for liver conditions, such as hepatitis. It’s usually measured together with alanine aminotransferase (ALT) According to liver specialists, abnormal ALT results are more likely related to liver injury than abnormal AST results. In fact, if AST levels are abnormal and ALT levels are normal, the problem is much more likely due to a heart condition or muscle problem rather than the liver. In some cases, the AST-to-ALT ratio may help your doctor diagnose certain liver diseases.

Your doctor may order an AST test for several reasons:

You’re experiencing the symptoms of liver disease

The symptoms of liver disease that may cause your doctor to order an AST test include:

  • fatigue
  • weakness
  • a loss of appetite
  • nausea
  • vomiting
  • swelling of your abdomen
  • yellow skin or eyes, which is called jaundice
  • dark urine
  • severe skin itching, or pruritus
  • bleeding difficulties
  • abdominal pain

You’re at risk for liver conditions

Your doctor may order this test if you’re at high risk of developing liver problems. Your liver plays important roles in your body, including making proteins and removing toxins. You can have mild liver damage and not show any signs or symptoms. Your doctor may order the AST test to screen you for liver inflammation or injury.

Factors that increase your risk of having liver problems include:

  • exposure to viruses that cause hepatitis
  • heavy alcohol or drug use
  • a family history of liver disease
  • diabetes
  • being overweight

Your doctor wants to monitor an existing liver condition

Your doctor can use the AST test to check the status of a known liver disorder. They can use it to check the effectiveness of treatment as well. If it’s being used to monitor liver disease, your doctor may order it periodically while you’re being treated. This will help them determine whether or not your treatment is working.

Your doctor wants to check that medications aren’t causing liver damage

Your doctor can use AST testing to make sure the medications you’re taking aren’t causing liver injury. If the AST test results suggest liver damage, your doctor may need to change your medications or lower your dose to help reverse any inflammation.

Your doctor wants to check if other health conditions are affecting your liver

The liver can become injured and the AST level may be abnormal if you have any of these conditions:

The AST test is performed on a blood sample. A healthcare provider usually takes the sample from a vein in your arm or hand using a small needle. They collect the blood in a tube and send it to a lab for analysis. Your doctor will inform you about your results when they become available.

Although no special preparations are necessary for the AST test, you should always tell your doctor about any medications you’re taking prior to a blood draw.

The risks of the AST test are minimal. You may experience some discomfort when the blood sample is drawn. You may have pain at the puncture site during or after the test.

Other potential risks of a blood draw include:

  • difficulty obtaining a sample, resulting in multiple needle sticks
  • excessive bleeding at the needle site
  • fainting due to the needle stick
  • an accumulation of blood under your skin, or a hematoma
  • an infection at the puncture site

AST test results vary based on the laboratory completing the analysis, and the typical ranges reported. The ranges for normal levels also differ depending on your sex and age. Recent research has shown that even mild increases in AST can be a sign of a liver problem that requires further investigation. The American College of Gastroenterology recommends that all abnormal AST results receive follow up.

Possible liver conditions based on levels of AST elevation

  • AST results outside of expected range and less than 5x expected range: hepatitis B, hepatitis C, alcoholic and nonalcoholic fatty liver, hemochromatosis, Wilson’s disease, autoimmune hepatitis, alpha-1 antitrypsin deficiency, medication
  • AST results between 5 to 15x expected range: acute viral hepatitis, any of the conditions related to lower levels of AST changes
  • AST results more than 15x expected range: acetaminophen (Tylenol) poisoning, shock liver (loss of liver blood supply)

Your doctor will talk to you about your results and what they mean. Your doctor will likely take a thorough medical history and perform a physical exam to determine if other conditions not related to the liver may be causing the abnormalities. Abnormal tests are often repeated to ensure the results are reproducible and accurate. Other tests are typically required to follow up abnormal AST levels. These can include further blood tests, liver imaging, and liver biopsy.

Some of the other conditions that cause AST levels in your liver to be abnormal are:

  • cirrhosis
  • liver cancer
  • autoimmune diseases
  • certain genetic disorders
  • nonalcoholic fatty liver disease (NAFLD)
  • liver trauma in physical injury

Other possible reasons for an increased AST level that aren’t related to the liver include:

  • a recent heart attack
  • strenuous activity
  • an injection of medicine into your muscle
  • burns
  • seizures
  • surgery
  • celiac disease
  • muscle diseases
  • abnormal red blood cell destruction

Levels of AST may also be elevated as a result of exposure to drugs or other substances that are toxic to your liver.

Depending on the reason for the test and your results, your doctor may recommend additional tests. If your AST test result shows elevated levels, your doctor may compare it with the results of other liver tests to help determine which form of liver disease you may have. These include tests for ALT, levels of alkaline phosphatase, albumin, and bilirubin. Blood clotting functions may also be checked, such as PT, PTT, and INR. Your doctor may also recommend an ultrasound or CT scan of your liver to help identify other reasons for abnormal tests.

Once you know which form of liver disease is causing the damage to your liver, you and your doctor can work together to come up with a treatment plan that meets your needs.