[Aspartate aminotransferase (AST)
The Test Sample
What is being tested?
Aspartate aminotransferase (AST) is an enzyme found in cells throughout the body but mostly in the heart and liver, and to a lesser extent in the kidneys and muscles. In healthy individuals, levels of AST in the blood are low. When liver or muscle cells are injured, they release AST into the blood. This makes AST a useful test for detecting liver damage.
The liver is a vital organ located in the upper right-hand side of the abdominal area. It is involved in many important functions in the body. The liver helps to process the body's nutrients, manufactures bile to help digest fats, produces many important proteins such as blood clotting factors, and breaks down potentially toxic substances into harmless ones that the body can use or excrete.
A number of conditions can cause injury to liver cells and may cause increases in AST levels. The test is most useful in detecting liver damage due to hepatitis, drugs toxic to the liver, cirrhosis, and alcoholism. AST, however, it is not specific for the liver and may be increased in conditions affecting other parts of the body.
How is the sample collected for testing?
A blood sample is drawn by needle from a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
The Test
1. How is it used?
2. When is it ordered?
3. What does the test result mean?
4. Is there anything else I should know?
How is it used?
The blood test for aspartate aminotransferase (AST) is usually used to detect liver damage. It is often ordered in conjunction with another liver enzyme, alanine aminotransferase (ALT), or as part of a liver panel to screen for and/or help diagnose liver disorders. AST and ALT are considered to be two of the most important tests to detect liver injury, although ALT is more specific than AST. Sometimes AST is compared directly to ALT and an AST/ALT ratio is calculated. This ratio may be used to distinguish between different causes of liver damage.
AST levels are often compared with results of other tests, such as alkaline phosphatase (ALP), total protein, and bilirubin to help determine which form of liver disease is present.
AST is often measured to monitor treatment of persons with liver disease and may be ordered either by itself or along with other tests for this purpose.Sometimes AST may be used to monitor people who are taking medications that are potentially toxic to the liver. If AST levels increase, then the person may be switched to another medication.
When is it ordered?
An AST test is ordered along with several other tests to evaluate a person who has signs and symptoms of a liver disorder. Some of these symptoms include:
• Weakness, fatigue
• Loss of appetite
• Nausea, vomiting
• Abdominal swelling and/or pain
• Jaundice
• Dark urine, light colored stool
• Itching (pruritus)
AST may also be ordered, either by itself or with other tests, for people who are at an increased risk for liver disease. Some examples include:
• Persons who might have been exposed to hepatitis viruses
• Those who are heavy drinkers
• Persons who have a history of liver disease in their family
• Persons taking drugs that can occasionally damage the liver
• Persons who are overweight and/or have diabetes
Persons who have mild symptoms, such as fatigue, may be tested for ALT to make sure they do not have chronic liver disease.
When AST is used to monitor treatment of persons with liver disease, it may be ordered on a regular basis during the course of treatment to determine whether the therapy is effective.
What does the test result mean?
Normally, levels of AST in the blood are low.
Very high levels of AST (more than 10 times the highest normal level) are usually due to acute hepatitis, often due to a virus infection. In acute hepatitis, AST levels usually stay high for about 1–2 months but can take as long as 3–6 months to return to normal. Levels of AST may also be markedly elevated as a result of exposure to drugs or other substances that are toxic to the liver as well as in conditions that cause decreased blood flow (ischemia) to the liver.
In chronic hepatitis, AST levels are usually not as high, often less than 4 times the highest normal level. In chronic hepatitis, AST often varies between normal and slightly increased, so doctors typically will order the test frequently to determine the pattern. Such moderate increases may also be seen in certain diseases of the liver, especially when the bile ducts are blocked, or with cirrhosis and certain cancers of the liver. AST is may also increased after heart attacks and with muscle injury, usually to a much greater degree than is ALT.
In most types of liver disease, the ALT level is higher than AST, and the AST/ALT ratio will be low. There are a few exceptions. The AST/ALT ratio is usually increased in alcoholic hepatitis, cirrhosis, and in the first day or two of acute hepatitis or injury from bile duct obstruction.
AST is often performed together with the ALT test or as part of a liver panel. For more about AST results in relation to other liver tests, see the Liver Panel article.
Is there anything else I should know?
Pregnancy may decrease AST levels.
A shot or injection of medicine into muscle tissue, or even strenuous exercise, may increase AST levels.
In rare instances, some drugs can damage the liver or muscle, increasing AST levels. This is true of both prescription drugs and some "natural" health products. Be sure to tell your doctor about all the drugs and health supplements you are taking.
Common Questions
1. What conditions other than liver problems can cause increased AST?
2. What other tests may be used to help determine the cause of liver damage?
1. What conditions other than liver problems can cause increased AST?
Conditions that affect other organs, such as the heart and skeletal muscle, can cause elevations of AST. Mild to moderate increases may be seen with vigorous excercise and muscle injury or in conditions such as acute pancreatitis and heart attacks.
2. What other tests may be used to help determine the cause of liver damage?
After a thorough physical exam and evaluation of a person's medical history, there are several other tests that may be performed as follow up depending on what is suspected to be the cause of liver damage. Some of these include:
• Tests for hepatitis A, B, and C
• Testing for exposure to drugs and other substances toxic to the liver (Drugs of Abuse Testing and Emergency of Overdose Drug Testing)
• Ethanol level
• Copper and ceruloplasmin for Wilson's disease
• Iron tests and genetic tests for hereditary hemochromatosis
• A liver biopsy
The Test Sample
What is being tested?
Aspartate aminotransferase (AST) is an enzyme found in cells throughout the body but mostly in the heart and liver, and to a lesser extent in the kidneys and muscles. In healthy individuals, levels of AST in the blood are low. When liver or muscle cells are injured, they release AST into the blood. This makes AST a useful test for detecting liver damage.
The liver is a vital organ located in the upper right-hand side of the abdominal area. It is involved in many important functions in the body. The liver helps to process the body's nutrients, manufactures bile to help digest fats, produces many important proteins such as blood clotting factors, and breaks down potentially toxic substances into harmless ones that the body can use or excrete.
A number of conditions can cause injury to liver cells and may cause increases in AST levels. The test is most useful in detecting liver damage due to hepatitis, drugs toxic to the liver, cirrhosis, and alcoholism. AST, however, it is not specific for the liver and may be increased in conditions affecting other parts of the body.
How is the sample collected for testing?
A blood sample is drawn by needle from a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
The Test
1. How is it used?
2. When is it ordered?
3. What does the test result mean?
4. Is there anything else I should know?
How is it used?
The blood test for aspartate aminotransferase (AST) is usually used to detect liver damage. It is often ordered in conjunction with another liver enzyme, alanine aminotransferase (ALT), or as part of a liver panel to screen for and/or help diagnose liver disorders. AST and ALT are considered to be two of the most important tests to detect liver injury, although ALT is more specific than AST. Sometimes AST is compared directly to ALT and an AST/ALT ratio is calculated. This ratio may be used to distinguish between different causes of liver damage.
AST levels are often compared with results of other tests, such as alkaline phosphatase (ALP), total protein, and bilirubin to help determine which form of liver disease is present.
AST is often measured to monitor treatment of persons with liver disease and may be ordered either by itself or along with other tests for this purpose.Sometimes AST may be used to monitor people who are taking medications that are potentially toxic to the liver. If AST levels increase, then the person may be switched to another medication.
When is it ordered?
An AST test is ordered along with several other tests to evaluate a person who has signs and symptoms of a liver disorder. Some of these symptoms include:
• Weakness, fatigue
• Loss of appetite
• Nausea, vomiting
• Abdominal swelling and/or pain
• Jaundice
• Dark urine, light colored stool
• Itching (pruritus)
AST may also be ordered, either by itself or with other tests, for people who are at an increased risk for liver disease. Some examples include:
• Persons who might have been exposed to hepatitis viruses
• Those who are heavy drinkers
• Persons who have a history of liver disease in their family
• Persons taking drugs that can occasionally damage the liver
• Persons who are overweight and/or have diabetes
Persons who have mild symptoms, such as fatigue, may be tested for ALT to make sure they do not have chronic liver disease.
When AST is used to monitor treatment of persons with liver disease, it may be ordered on a regular basis during the course of treatment to determine whether the therapy is effective.
What does the test result mean?
Normally, levels of AST in the blood are low.
Very high levels of AST (more than 10 times the highest normal level) are usually due to acute hepatitis, often due to a virus infection. In acute hepatitis, AST levels usually stay high for about 1–2 months but can take as long as 3–6 months to return to normal. Levels of AST may also be markedly elevated as a result of exposure to drugs or other substances that are toxic to the liver as well as in conditions that cause decreased blood flow (ischemia) to the liver.
In chronic hepatitis, AST levels are usually not as high, often less than 4 times the highest normal level. In chronic hepatitis, AST often varies between normal and slightly increased, so doctors typically will order the test frequently to determine the pattern. Such moderate increases may also be seen in certain diseases of the liver, especially when the bile ducts are blocked, or with cirrhosis and certain cancers of the liver. AST is may also increased after heart attacks and with muscle injury, usually to a much greater degree than is ALT.
In most types of liver disease, the ALT level is higher than AST, and the AST/ALT ratio will be low. There are a few exceptions. The AST/ALT ratio is usually increased in alcoholic hepatitis, cirrhosis, and in the first day or two of acute hepatitis or injury from bile duct obstruction.
AST is often performed together with the ALT test or as part of a liver panel. For more about AST results in relation to other liver tests, see the Liver Panel article.
Is there anything else I should know?
Pregnancy may decrease AST levels.
A shot or injection of medicine into muscle tissue, or even strenuous exercise, may increase AST levels.
In rare instances, some drugs can damage the liver or muscle, increasing AST levels. This is true of both prescription drugs and some "natural" health products. Be sure to tell your doctor about all the drugs and health supplements you are taking.
Common Questions
1. What conditions other than liver problems can cause increased AST?
2. What other tests may be used to help determine the cause of liver damage?
1. What conditions other than liver problems can cause increased AST?
Conditions that affect other organs, such as the heart and skeletal muscle, can cause elevations of AST. Mild to moderate increases may be seen with vigorous excercise and muscle injury or in conditions such as acute pancreatitis and heart attacks.
2. What other tests may be used to help determine the cause of liver damage?
After a thorough physical exam and evaluation of a person's medical history, there are several other tests that may be performed as follow up depending on what is suspected to be the cause of liver damage. Some of these include:
• Tests for hepatitis A, B, and C
• Testing for exposure to drugs and other substances toxic to the liver (Drugs of Abuse Testing and Emergency of Overdose Drug Testing)
• Ethanol level
• Copper and ceruloplasmin for Wilson's disease
• Iron tests and genetic tests for hereditary hemochromatosis
• A liver biopsy
