Aspartate 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:
- red blood cells
A small amount of AST is typically in your bloodstream. Higher-than-typical amounts of this enzyme in your blood may be a sign of a health problem. Atypical 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
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) test.
Doctors commonly use the AST test to check for liver conditions, such as hepatitis. AST is usually measured together with alanine aminotransferase (ALT). According to liver specialists, atypical ALT results are more likely related to liver injury than atypical AST results.
In fact, if AST levels are elevated and ALT levels are normal, the problem is much more likely due to a condition of the heart, muscle, kidney, or destruction of red blood cells (hemolysis) 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:
- a loss of appetite
- 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
- frequent alcohol or drug use
- a family history of liver disease
- 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 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 atypical if you have any of these conditions:
The AST test is performed on a blood sample. A healthcare professional 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
For certain types of blood tests, you may need to fast or stop taking certain medications for several hours leading up to the test. There is usually no need for this prior to an AST test.
Drinking plenty of water before your test will make it easier for the technician to access your veins. Remember to wear a top that will allow easy access to your arms.
Make sure your doctor knows what medications you are taking when the AST test is scheduled. They will be able to give you any special instructions that might pertain to your specific needs.
AST test results vary based on the laboratory completing the analysis and the typical ranges reported. The ranges for typical levels also differ depending on 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 atypical AST results receive a follow-up.
AST normal range
AST results are generally measured in units per liter (U/L).
|Age||Healthy range||Atypical range|
|newborn||47–150 U/L||<47 or >150 U/L|
|children||9–80 U/L||<9 or >80 U/L|
|adult men||14–20 U/L||<14 or >20 U/L|
|adult women||10–36 U/L||<9 or >36 U/L|
Healthy AST levels have a lower maximum in adults than in newborns and children. AST levels decrease slightly during pregnancy.
On the extreme end of the spectrum, AST levels could surpass 20,000 U/L.
Possible liver conditions based on levels of AST elevation
- AST results outside of the expected range and less than 5 times the expected range:
- AST results between 5 to 15 times the expected range:
- acute viral hepatitis
- any of the conditions related to lower levels of AST changes
- AST results that are more than 15 times the expected range:
- acetaminophen (Tylenol) poisoning
- shock liver (loss of liver blood supply)
Your doctor will speak with you about your results and what they mean. They 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 atypical characteristics.
Atypical tests are often repeated to ensure the results are reproducible and accurate. Other tests are usually required to follow up atypical AST levels. These can include:
- further blood tests
- liver imaging
- liver biopsy
Some of the other conditions that cause atypical AST levels in your liver are:
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
- celiac disease
- muscle diseases
- atypical 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. Your doctor may also recommend an ultrasound or CT scan of your liver to help identify other reasons for atypical 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.