AST and ALT are considered to be two of the most important tests to detect liver injury, although ALT is more specific to the liver than is 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 and to help recognize heart or muscle injury.
ALT may also be ordered, either by itself or with other tests, for people who are at an increased risk for liver disease since many people with mild liver damage will have no signs or symptoms. Some examples include:
Very high levels of ALT (more than 10 times normal) are usually due to acutehepatitis, sometimes due to a viral infection. In acute hepatitis, ALT levels usually stay high for about 1-2 months but can take as long as 3-6 months to return to normal. Levels of ALT may also be markedly elevated (sometimes over 100 times normal) 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.
ALT levels are usually not as high in chronic hepatitis, often less than 4 times normal. In this case, ALT levels often vary between normal and slightly increased, so the test may be ordered frequently to see if there is a pattern. Other causes of moderate increases in ALT include obstruction of bile ducts, cirrhosis (usually the result of chronic hepatitis or bile duct obstruction), heart damage, alcohol abuse, and with tumors in the liver.
In most types of liver diseases, the ALT level is higher than AST, and the AST/ALT ratio will be low ( less than 1). There are a few exceptions; the AST/ALT ratio is usually greater than 1 in alcoholic hepatitis, cirrhosis, and with heart or muscle injury and may be greater than 1 for a day or two after onset of acute hepatitis.
ALT is often performed together with a test for AST or as part of a liver panel. For more about ALT results in relation to other liver tests, see the Liver Panel article.
A shot or injection of medicine into the muscle tissue, or strenuous exercise, may increase ALT levels.
Many drugs may raise ALT levels by causing liver damage in a very small percentage of patients taking the drug. This is true of both prescription drugs and some "natural" health products. Be sure to tell your health practitioner about all of the drugs and/or health supplements you are taking.
This article was last reviewed on October 29, 2013. | This article was last modified on February 24, 2015.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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