Aspartate aminotransferase (AST) is an enzyme that’s present in various parts of the 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 muscles, heart, and liver. A small amount of AST is typically in the bloodstream. Higher-than-normal amounts of this enzyme in your blood may be a sign of a health problem.
AST levels increase when there’s damage to the tissues and cells where the enzyme is found. The levels directly reflect the amount of damage in that area. AST levels rise six to 10 hours after damage occurs and remain high for about four days after a sudden injury. AST levels can be elevated at birth, generally decrease with age into adulthood, and then increase slightly in older adults.
The AST test measures the amount of AST in your blood. The test is also known as a serum glutamic-oxaloacetic transaminase (SGOT) test.
Doctors commonly use the AST test to check for liver diseases, such as hepatitis. It’s usually measured together with alanine aminotransferase (ALT). The AST to ALT ratio can help your doctor diagnose liver disease. Your doctor can use the ratio to help them determine if there’s been damage to your liver as opposed to damage to your heart or muscles. AST and ALT are two of the most important tests used to detect injury within the cells of the liver.
Your doctor may order an AST test for several reasons:
If you’re experiencing the symptoms of liver disease
The symptoms of liver disease that may cause your doctor to order an AST test include:
- a loss of appetite
- swelling of the abdomen
- yellow skin or eyes, which is called jaundice
- dark urine
- severe skin itching, or pruritus
If you’re at risk for liver conditions
Your doctor may order this test if you’re at high risk of developing liver problems. The liver plays important roles in the body, including making proteins and removing toxins. You can have mild liver damage and not show any signs or symptoms. They may order the AST test to help them find any hidden issues if you’re at an increased risk for liver disease.
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
- being overweight
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 your treatment is working or not.
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 damage. If the AST test results suggest liver damage, your doctor can tweak your medications to prevent any further damage.
To check if other health conditions are affecting your liver
The AST level may be abnormal if you have any of these conditions:
- kidney failure
- inflammation of the pancreas, or pancreatitis
- certain viral infections, such as mononucleosis
- gallbladder disease
The AST test is performed on a blood sample. A healthcare provider usually takes it from a vein in the arm or hand using a small needle. They’ll 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.
No special preparations are necessary for the AST test. You should always tell your doctor about any medications you’re taking.
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 blood loss
- an accumulation of blood under the skin, or a hematoma
- an infection at the puncture site
AST test results will vary based on the laboratory completing the analysis. The ranges for normal levels also differ depending on your sex and age. Your doctor will talk to you about your results and what they mean. Elevated AST levels could be a sign of liver damage.
People with acute viral hepatitis can have AST levels that are more than 10 times the normal amount. Acute viral hepatitis is sudden inflammation of the liver due to infection by one of the several viruses that cause hepatitis. Acute viral hepatitis over time can become chronic hepatitis. In these cases, AST continues to stay abnormal but at much lower levels.
Some of the other conditions that cause AST levels in the liver to be abnormal are:
- liver cancer
- autoimmune diseases
- certain genetic disorders
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
Levels of AST may also be extremely elevated as a result of exposure to drugs or other substances that are toxic to the 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 results of other tests to help determine which form of liver disease you have. These include tests for levels of alkaline phosphatase, total protein, and bilirubin.
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 works for you.