Aspartate Aminotransferase (AST)
- Also Known As:
- Serum Glutamic-Oxaloacetic Transaminase
- Aspartate Transaminase
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Test Quick Guide
Aspartate aminotransferase (AST) is an enzyme. Enzymes are types of proteins that enable most bodily processes. AST exists mostly in the liver, but it is found in numerous tissues in the body.
When cells become damaged, AST can be released into the bloodstream. For this reason, abnormal levels of AST in a blood sample can be an indication of an underlying problem.
Although AST can be measured alone, it is usually included with other enzymes as part of broader tests, such a liver panel or comprehensive metabolic panel (CMP). When interpreted alongside other enzymes, an AST measurement can help identify liver disease and other health issues.
About the Test
Finding an Aspartate Aminotransferase Test
How to get tested
Tests for AST are usually prescribed by a doctor and conducted in a doctor’s office, hospital, or laboratory where blood is drawn from a vein in your arm. Results are determined through laboratory analysis of your blood sample.
Can I take the test at home?
While most AST testing is done with a blood draw in a medical setting, some at-home tests are available that include a measurement of AST in a panel along with other enzymes and proteins. For these tests, you take a blood sample at home and then mail it to a laboratory. You then receive results by mail, with a smartphone app, or through an online portal.
How much does the test cost?
The cost of an AST test can vary depending on where the test sample is taken, whether other measurements are included, whether you have medical insurance, and whether your insurance is covering the test.
There may be several different types of charges associated with an AST test or a panel test that includes AST. For example, separate fees may be charged by the technician who draws your blood, the lab that does the analysis, and the office of the doctor who prescribes the test or reviews the results with you.
Many of these charges are at least partially paid for by insurance if your doctor is recommending the test, but you should check with your doctor and insurance company to find out if your test will be covered and if you are responsible for any copayment or deductible.
At-home tests that include AST can vary in price based on how many different measurements are taken. Tests are often available for around $100, which includes the test kit, shipping, laboratory analysis, and results.
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Taking an Aspartate Aminotransferase Test
Testing aspartate aminotransferase requires a sample of blood. Blood is obtained by using a procedure called venipuncture using a needle that is inserted into a vein in your arm.
At-home tests for AST also rely on a blood sample; however, they utilize a fingerstick instead of venipuncture. This means that you prick your finger to obtain a drop of blood. This sample is then mailed to a laboratory where it can be tested for its level of AST.
Before the test
Because AST is usually measured with other enzymes and compounds, you typically need to fast before your blood is drawn. This means that you consume no food and no beverages other than water. You may need to fast for up to 12 hours before the test, but you should check with your doctor’s office for specific instructions.
If you are being tested for only AST, you usually do not need to fast or take any other special precautions before the test.
Various types of medications can influence levels of AST and other liver enzymes, so you should talk with your doctor before the test about any prescription drugs, over-the-counter medications, or dietary supplements that you take regularly.
During the test
When you go for a blood draw, you will be seated, and a stretchy band will be tied tightly around the upper part of one arm so that there is greater blood flow in that arm. The technician will use an antiseptic to clean the puncture site and then insert a needle into your vein to withdraw a vial of blood.
Once the necessary amount of blood is drawn, the needle is removed. The whole process is usually over within a few minutes. You may experience a sting or other pain from the needle puncture.
For an at-home test, you will need to read and follow the instructions in your test kit. In most cases, you will use an antiseptic to clean your fingertip and then use a small needle included in the kit to lightly prick your finger. A drop of blood is placed on a special test paper, which you then seal and put in the mail.
After the test
After a blood draw, a small bandage will be placed on your arm to apply pressure and stop further bleeding. You may have some bruising or discomfort, but it is rare for there to be any serious side effects.
If you were instructed to fast before the test, you may want to bring a snack to eat once the test is over. You can return to most normal activities, including driving, after the test.
Side effects are also uncommon after an at-home test. If needed, you can use a bandage to stop continued bleeding from your fingertip.
Aspartate Aminotransferase Test Results
Receiving test results
You should receive results with your AST levels within a few business days after your blood draw. A test report may be available to access electronically or sent to you by mail. Your doctor’s office may also call you to provide results.
If you take an at-home AST test, the test kit must be sent by mail to a laboratory where it can be analyzed. As a result, it may take an extra few days to get results, which are usually provided electronically.
Interpreting test results
AST levels are usually listed on your test report in units per liter (U/L) or international units per liter (IU/L). Next to the level found in your blood, the test report should list the laboratory’s reference range.
It is important to look closely at the range for the specific lab that analyzed your sample because there is no universal reference range for AST. Ranges can vary because not all labs use the same methods and because studies have not demonstrated a precise healthy range.
In addition, there is no AST level that is normal for all people. Instead, a healthy AST level can change depending on your age, sex, race, weight, and other factors that your doctor can consider when interpreting your test result.
To understand the significance of your results, your doctor often looks not only at AST but also the levels of other enzymes that are included in a liver panel test. Patterns in which enzymes are normal or abnormal can offer meaningful clues about an underlying problem.
Because AST levels in the blood can rise when cells are damaged, elevated AST can reflect health conditions, including liver diseases like cirrhosis or hepatitis. To try to determine the cause of an abnormal result, the doctor may consider how high the AST level is and how it compares to the levels of other liver enzymes.
Very high levels of AST often reflect short-term liver damage while smaller but persistent elevations in AST over time can be tied to chronic conditions. However, because AST is found in other parts of the body, it can be elevated in the blood as a result of cell damage outside the liver.
For this reason, the doctor may look at the levels of both AST and the enzyme alanine aminotransferase (ALT) side by side. ALT is more concentrated in the liver, so if AST is high while ALT is normal, it can be a sign of a problem outside the liver. In other cases, though, having a much higher level of AST than ALT can be a sign of alcohol-induced damage to the liver.
It is also important to note that, by itself, having elevated AST is not proof of a medical problem. It is possible for healthy people with proper liver function to have an AST level outside the normal range, which can occur based on individual factors like age, sex, race, diet, exercise, or having taken medications that can affect AST.
Because of the complexity of interpreting AST levels, including their relationship to other measurements on a panel test, you should always discuss your test result with a doctor who can explain what the test means and how it reflects your overall health.
Are test results accurate?
Laboratory tests for AST are considered to be very reliable. No test is perfectly accurate, but methods of AST testing allow for results that are generally consistent and dependable for medical interpretation and use.
Do I need follow-up tests?
If your AST levels are abnormal, there are a number of follow-up tests that can be prescribed depending on your circumstances. Sometimes a doctor will recommend ongoing monitoring with repeat tests at a set interval. In other cases, other blood tests, imaging tests, or a biopsy may be used to either diagnose or rule out health conditions that could be associated with an abnormal AST test result.
Questions for your doctor about test results
To best understand the meaning and interpretation of your AST test, you can bring up some of the following questions when discussing your test with your doctor:
- What is the reference range for AST for the laboratory that did my test?
- Were my AST levels normal or abnormal?
- Did the test measure anything in addition to AST? Were any of those levels abnormal?
- What is the most likely explanation for my AST level?
- Should I repeat this test or take any other tests as a follow-up?
Aspartate aminotransferase is frequently tested along with several different measurements. The following sections provide more information about how AST is different from several related tests.
How is aspartate aminotransferase different from a liver panel test?
A liver panel is a test with several components that provides detail about the status of the liver. A liver panel includes AST but also measures alanine aminotransferase (ALT), alkaline phosphatase (ALP), albumin, and bilirubin.
AST is much more frequently tested as part of the liver panel than it is tested alone.
How is aspartate aminotransferase different from alanine aminotransferase (ALT)?
Alanine aminotransferase, often known as ALT, is an enzyme that is commonly measured along with AST.
While both are known as liver enzymes, AST is found in more parts of the body than ALT. For this reason, abnormal levels of ALT tend to be a better indicator of liver problems than AST, but doctors usually review both of these levels together when interpreting a panel test or assessing the condition of the liver.
How is aspartate aminotransferase different from alkaline phosphatase (ALP)?
AST and ALP are components of the standard liver panel and the comprehensive metabolic panel. Like AST, ALP is an enzyme that s also found in many parts of the body.
When evaluating liver health, AST is generally used to detect damage to liver cells while ALP is more often used to identify a blockage of the bile ducts in and around the liver. In addition, ALP is found in the bones, so ALP testing is more common in the diagnosis of bone disorders.
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