Aspartate Transferase (AST)
What is aspartate transferase (AST)?
Aspartate transferase (AST), also known as aspartate aminotransferase, is an enzyme that exists in your liver, heart, brain, pancreas, kidneys, muscles and many tissues in your body. Although it can be found throughout your body, AST is most commonly associated with liver health.
An enzyme is a type of protein in a cell that acts as a catalyst and allows certain bodily processes to happen. There are thousands of different enzymes throughout your body that have important functions.
What is an AST blood test?
An AST blood test measures the amount of aspartate transferase in your blood. In most cases, your healthcare provider uses an AST blood test to help assess the health of your liver, but it can provide insight into other health conditions as well.
When your cells get damaged, AST can leak into your bloodstream. Because of this, high levels of AST in a blood sample can be a sign of an underlying medical condition — most often (but not always), a liver condition.
As many types of liver conditions can cause AST levels in your blood to rise, healthcare providers don’t use the test alone to diagnose conditions. An AST blood test is most often included in a blood test panel, such as a liver enzyme panel (HFP) or a comprehensive metabolic panel (CMP). A blood panel measures several aspects of your blood with one sample and can provide more detailed information about your overall health.
Common names for an AST blood test include:
- Aspartate transferase (AST).
- Aspartate aminotransferase (AST).
- Serum glutamic-oxaloacetic transaminase.
- Aspartate transaminase.
How is aspartate transferase (AST) different from alanine transferase (ALT)?
Alanine transferase (ALT) is an enzyme that’s commonly measured along with AST in a liver function panel or comprehensive metabolic panel (CMP). Both these enzymes can leak into your bloodstream when certain cells in your body are damaged.
While both are known as liver enzymes, AST is found in more parts of your body than ALT. For this reason, higher-than-normal levels of ALT tend to be a more specific indicator of liver conditions than higher-than-normal AST levels. However, your healthcare provider will usually review both these levels together when assessing the health of your liver.
Why do I need an AST blood test?
The purpose of an AST blood test is to detect damage to cells. If cells in your liver are damaged, it can cause AST to leak into your blood, so an AST blood test can help find liver issues. While your healthcare provider will most often use the test to help assess liver health, an AST test can also provide information for other medical conditions and cell damage elsewhere in your body.
Your healthcare provider may order a blood panel test that includes an AST test for you to help screen for, monitor or help diagnose liver conditions and other medical conditions.
Screening means checking for potential health issues before you experience symptoms. Your healthcare provider will likely recommend screening with a liver panel blood test that includes an AST test if you have risk factors for liver disease, including:
- Heavy alcohol use.
- Family history of liver disease.
- Injecting drugs using shared needles.
Since AST tests are often included in routine blood panel tests that assess your general overall health, such as a comprehensive metabolic panel, you may get an AST test even if you don’t have risk factors for liver disease.
If you have a liver condition, your healthcare provider may order an AST test, often as part of a panel, to monitor your condition to see if it’s improving, worsening or staying the same with or without treatment. Your healthcare provider may also have you do an AST test and liver enzyme panel test if you’re taking a medication that can affect your liver.
Your healthcare provider may use an AST test for diagnostic purposes when you’re experiencing signs and symptoms of possible liver problems. While healthcare providers can’t diagnose a condition based solely on AST levels, it can be an important part of the diagnostic process.
Signs and symptoms of liver conditions include:
- Nausea and/or vomiting.
- Belly (abdominal) pain.
- Itchy skin.
- Jaundice (a yellowing of your skin and the whites of your eyes).
- Tiredness (fatigue).
- Appetite loss.
Who performs an AST blood test?
A phlebotomist usually performs blood draws, including those for an AST blood test, but any healthcare provider who is trained in drawing blood can perform this task. They then send the samples to a lab where a medical laboratory scientist prepares the samples and performs the tests on machines known as analyzers.
Do I need to fast for an AST blood test?
If your AST test is part of a comprehensive metabolic panel (CMP), you’ll likely need to fast for 10 to 12 hours before your CMP blood test. Fasting means not eating or drinking anything other than water.
It’s not as common, but if you’re only getting an AST blood test or a hepatic function panel (HFP), you don’t need to fast.
In any case, your healthcare provider will give you instructions when they order the bloodwork. Be sure to follow their directions.
Do I need to do anything to prepare for an AST blood test?
Many different types of medications and supplements can affect your AST levels, so it’s important to tell your healthcare provider about any drugs or dietary supplements you’re taking before you get the test. In some cases, your healthcare provider may have you stop taking a medication before the test. Only stop taking medication if your healthcare provider tells you to do so.
What should I expect during my AST blood test?
You can expect the following during an AST blood test:
- You’ll sit in a chair, and your healthcare provider will check your arms for an easily accessible vein. This is usually in the inner part of your arm on the other side of your elbow.
- Once they’ve located a vein, they’ll clean and disinfect the area.
- They’ll then insert a small needle into your vein to take a blood sample. This may feel like a small pinch.
- After they insert the needle, a small amount of blood will collect in a test tube.
- Once they have enough blood to test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop the bleeding.
- They’ll place a bandage over the site, and you’ll be finished.
The entire procedure usually takes fewer than five minutes.
What should I expect after my AST blood test?
After your healthcare provider has collected your blood sample, they’ll send it to a laboratory for testing. Once the test results are back, your healthcare provider will share the results with you.
What are the risks of an AST blood test?
Blood tests are a very common and essential part of medical testing and screening. There’s very little risk to having blood tests. You may have slight tenderness or a bruise at the site of the blood draw, but this usually resolves quickly.
When can I expect the results of my AST blood test?
In most cases, you should have your test results within one to two business days, though it could take longer.
Results and Follow-Up
What do the results of an AST blood test mean?
Blood test reports, including aspartate transferase (AST) test reports, usually provide the following information:
- The name of the blood test or what was measured in your blood.
- The number or measurement of your blood test result.
- The normal measurement range for that test.
- Information that indicates if your result is normal or abnormal or high or low.
What is the normal range for an AST blood test?
The normal range for aspartate transferase (AST) varies from laboratory to laboratory. One common reference range for an AST blood test is 8 to 33 U/L (units per liter). As ranges can vary depending on the laboratory, it’s important to check your test result report to see what your specific lab’s reference range is.
It’s also important to know that there’s no AST range that’s normal for all people. A healthy AST level can change depending on several factors, including:
- Your age.
- Your sex.
- Your race.
- Your weight.
Your healthcare provider will consider all these factors when interpreting your test result.
What does it mean if my AST level is high?
An elevated AST level may be a sign of a liver condition. Liver disease is even more likely when the results of other liver blood tests are also abnormal. Although it’s not as common, elevated AST levels can be caused by cell damage in other areas of your body as well.
A high AST level may indicate any of the following liver conditions:
- Alcohol-induced liver injury.
- Hepatitis (liver inflammation).
- Cirrhosis (scarring of the liver).
- Taking medications that are toxic to your liver.
- Liver tumor or liver cancer.
- Liver ischemia (not enough blood flow to your liver, which leads to death of liver tissue).
A high AST level may also indicate any of the following conditions that aren’t directly related to your liver:
- Hemochromatosis (having too much iron in your body, which damages your heart, liver and pancreas).
- Heart attack (myocardial infarction).
- Mononucleosis ("mono").
- Muscle disease.
Your AST levels can also increase temporarily after the following events:
People who are pregnant may also have increased levels of AST.
It’s important to understand that having a high AST test result does not necessarily mean you have a medical condition. Other factors can affect your AST levels. Your healthcare provider will consider several factors, including other blood test results and your medical history, when analyzing your results.
Should I be worried if I have a high AST test result?
If your AST test result is higher than the given normal range on your report, it doesn’t necessarily mean that you have a medical condition that needs treatment. People with healthy and proper liver function can have an AST level outside of the normal range, which can happen due to several factors, including:
- Your age.
- Your sex.
- Your race.
- Your diet.
- Taking medications that can affect your AST levels.
- If you’re pregnant.
Your healthcare provider will take into consideration all these factors, including your other blood test results, when analyzing your AST levels and will let you know if you should undergo further testing.
Do I need follow-up tests if my AST results are abnormal?
Your healthcare provider may recommend follow-up tests if you have an abnormal AST level. Follow-up testing may include:
- Repeat AST blood tests.
- Other blood tests.
- Imaging tests.
- A biopsy.
When should I call my doctor?
If you’re experiencing symptoms of liver damage, such as jaundice or belly pain, call your healthcare provider.
If you’ve been diagnosed with a liver condition and are experiencing new or concerning symptoms, contact your healthcare provider.
If you have any questions about your aspartate transaminase (AST) results, don’t be afraid to ask your healthcare provider questions.
A note from Cleveland Clinic
Seeing an abnormal test result can be stressful. Know that having a high level of aspartate transaminase (AST) doesn’t necessarily mean you have a medical condition and need treatment. Many factors can affect your AST levels, and approximately 1 in 20 healthy people will have a result outside the normal reference range. Your healthcare provider will let you know if you need to undergo further tests to determine the cause of an abnormal level. And, don’t be afraid to ask your healthcare provider questions. They’re there to help you.
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