AST
The Test
How is it used?
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?
- Weakness, fatigue
- Loss of appetite
- Nausea, vomiting
- Abdominal swelling and/or pain
- Jaundice
- Dark urine, light colored stool
- Itching (pruritis)
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?
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?
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.
