An AST blood test measures levels of aspartate aminotransferase (AST) and helps determine liver function. Too much of this enzyme can indicate a problem, such as liver damage.
Aspartate aminotransferase (AST) is an enzyme mostly found in the liver. AST is also present in other parts of the body, including the:
- kidneys
- heart
- muscles
Another name for the AST enzyme is serum glutamic-oxaloacetic transaminase (SGOT).
Most people have low levels of the AST enzyme. Damage to liver cells can cause the release of extra AST into the blood though, leading to higher levels of the enzyme.
After taking a blood test, doctors will classify AST ranges as normal, high, or low. Laboratories may use different testing methods for analyzing samples, so normal ranges can vary between each laboratory.
There is not an exact range for AST levels, as levels can vary among people and still be normal. AST levels can vary depending on factors such as:
- age
- sex
- weight
- race
The measurements for AST levels are typically in units per liter (U/L) or international units per liter (IU/L). On a test result, the laboratory will usually list their specific reference range.
People will need to look at this reference range and discuss with their doctor what their test results mean for them. To understand the results of an AST blood test, a doctor will also look at other enzymes that can indicate a liver problem.
The following table indicates general AST blood test ranges. However, reference ranges can vary slightly among different laboratories.
| Adults | Children | |
|---|---|---|
| Normal | <36 U/L | 10–40 IU/L |
| High | >36 U/L >1,000 U/L are very high levels and may be a sign of liver injury or hepatitis | >40 IU/L which may be a sign of liver inflammation |
Results from an AST blood test can help indicate liver health.
If AST levels are high, it may also be a sign of:
- chronic hepatitis
- damage from alcohol
- cholestasis, a decrease in bile flow
- heart, kidney, bone, or muscle damage
- liver cancers
- liver scarring, known as liver cirrhosis
Very high AST levels are usually a sign of progressing liver damage, often due to acute hepatitis.
Low AST levels may indicate:
- vitamin B6 deficiency
- kidney disease
- liver disease
- cirrhosis
- cancer
- autoimmune conditions
- genetic conditions
A doctor may also test levels of alanine aminotransferase (ALT), another liver enzyme. ALT levels occur in higher concentrations in the liver.
If ALT levels are normal but AST levels are high, it could indicate a health problem outside of the liver, or it may be a sign of alcohol-induced liver damage.
Having high levels of AST and no other signs of a problem is not necessarily a cause for concern. People with normal liver function can have high AST levels, which may be due to:
- age
- sex
- race
- certain medications
A person should always discuss any medications or health products they take with a doctor.
Doctors primarily use the AST blood test to check for and assess liver problems, usually alongside other liver tests. The AST protein mainly occurs in the liver and heart. With liver damage, AST can leak from the liver into the bloodstream. When this happens, AST levels in the blood will be higher than normal.
AST also occurs in the brain, heart, kidneys, and muscles. If there is damage in any of these areas, AST levels may also increase.
To rule out issues affecting areas outside the liver, doctors may order a check of the second liver enzyme, ALT, at the same time. If both levels are high, it may indicate a problem with a person’s liver. If only AST levels are high, this may indicate a problem with another organ or system.
People may have an AST test for screening, diagnosis, or monitoring purposes. A doctor may recommend this test if a person:
- has risk factors for liver disease, such as family history, obesity, or diabetes
- has symptoms of a liver problem, such as jaundice, fatigue, or unexplained weight loss
- is undergoing treatment for a liver condition, as an AST blood test can help show how well treatment is working
Alanine aminotransferase (ALT) is an enzyme that mostly occurs in the liver. If there is damage to liver cells, ALT levels in the bloodstream can increase. An ALT test can help indicate liver health, along with other liver enzyme tests.
Healthcare professionals may use both ALT and AST tests to check for the presence of liver enzymes in the blood, as this can give them a clearer idea of overall liver function and health.
The AST blood test is straightforward and similar to any other blood test. A healthcare professional may take the following steps:
- sit the person down and tie a stretchy band around the upper arm to increase blood flow to that area
- clean the site of the blood draw with an antiseptic wipe
- insert a needle into a vein in the arm to take a blood sample, which may cause people to feel a mild prick or pain
- remove the needle once they have drawn enough blood
- send the blood sample to a laboratory for testing
An AST blood test will usually only take a few minutes in total.
In some cases, people may be able to take an AST test at home. Using an at-home test kit, people will take a blood sample from their fingertip and send the sample to a laboratory. People may receive AST blood test results through the mail, an app, or an online system.
Learn how long it might take to receive blood test results here.
Preparation
People may need to fast for several hours if they are having a combination of liver enzyme tests.
If people are only having an AST blood test, they may not need to fast or prepare in any way.
People will need to let their doctor know if they are taking any medications or supplements, as some may interfere with liver enzyme levels.
As a healthcare professional will be taking blood from the arm, it may be helpful to wear short sleeves during the test.
As with any blood test, an AST blood test has very few risks. It is rare to experience any severe side effects, but people may have some mild bruising or discomfort in the area at the site of the blood draw.
A healthcare professional will place a Band-Aid or bandage on the arm to stop any bleeding.
People may want to have something to eat after the test, particularly if they were fasting beforehand. It is safe for people to drive and continue their usual activities after an AST blood test, unless they experience any unusual symptoms.
A doctor may order tests along with an AST blood test or follow-up tests. This is to help ensure proper diagnosis and determine the best course of treatment. These tests
- ALT test: A doctor may order an ALT test alongside an AST test.
- Platelet count: Low platelet levels may indicate HELLP syndrome during pregnancy.
- Coagulation panel: This measures the functioning of clotting-related proteins that the liver produces.
- Complete metabolic panel: This assesses how well the kidneys and liver are working and shows levels of electrolytes.
- Bilirubin test: A bilirubin test checks levels of a byproduct created when the liver breaks down red blood cells.
- Glucose test: High or low blood glucose levels may indicate a liver problem.
- Viral testing: This can help doctors check for hepatitis.
- Imaging: A doctor may order images of the liver via ultrasound.
The extent of follow-up testing will depend on a person’s results. A doctor may also take additional blood tests, imaging tests, or a biopsy to identify or rule out any potential conditions relating to abnormal AST levels.
An AST blood test, or SGOT test, checks how much AST, a liver enzyme, is present in the blood. High levels of AST in the bloodstream could be a sign of liver damage, or cell damage in another organ such as the heart or kidneys.
Doctors may also take additional tests to check other liver enzymes, such as ALT, to get more information on the health of the liver.