How is it used?
The alanine aminotransferase (ALT) test is typically used to detect liver injury. It is often ordered in conjunction withaspartate aminotransferase (AST) as part of a liver panel or comprehensive metabolic panel (CMP) to screen for and/or help diagnose liver disease.
ALT is an found mostly in the cells of the liver and kidney. When the liver is damaged, ALT is released into the blood. This makes ALT a useful test for early detection of liver damage.
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 values are often compared to the results of other tests such as alkaline phosphatase (ALP), total protein, and bilirubinto help determine which form of liver disease is present.
ALT is often used to monitor the treatment of persons who have liver disease, to see if the treatment is working, and may be ordered either by itself or along with other tests for this purpose.
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When is it ordered?
ALT may be ordered as part of a comprehensive metabolic panel when a person has a routine health examination.
A healthcare practitioner usually orders an ALT test (and several others) to evaluate a person who has and of a liver disorder. Some of these signs and symptoms may include:
- Weakness, fatigue
- Loss of appetite
- Nausea, vomiting
- Abdominal swelling and/or pain
- Jaundice
- Dark urine, light-colored stool
- Itching ()
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. Even without other symptoms, ALT will be increased with mild liver damage. Some examples include:
- Persons who have a history of known or possible exposure to hepatitis viruses
- Those who are heavy drinkers
- Individuals whose families have a history of liver disease
- Persons who take drugs that might damage the liver
- Persons who are overweight and/or have diabetes
When ALT is used to monitor the treatment of people who have liver disease, it may be ordered on a regular basis during the course of treatment to determine whether the therapy is effective.
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What does the test result mean?
A low level of ALT in the blood is expected and is normal. Liver disease is the most common reason for higher than normal levels of ALT.
Very high levels of ALT (more than 10 times normal) are usually due to hepatitis, sometimes due to a 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 or in conditions that cause decreased blood flow () to the liver.
ALT levels are usually not as high in 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, (usually the result of chronic hepatitis or bile duct obstruction), heart damage, alcohol abuse, and with tumors in the liver.
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.
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.
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Is there anything else I should know?
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 healthcare provider about all of the drugs and/or health supplements you are taking.