ALT

The alanine aminotransferase (ALT) blood test is typically used to detect liver injury. It is often ordered in conjunction with aspartate aminotransferase (AST) or as part of a liver panel to screen for and/or help diagnose liver disease. 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.

ALT values are often compared to the results of other tests such as alkaline phosphatase (ALP), total protein, and bilirubin to 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.

A doctor usually orders an ALT test (and several others) to evaluate a person who has 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)

ALT 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 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 occasionally damage the liver
• Persons who are overweight and/or have diabetes

In persons with mild symptoms, such as fatigue or loss of energy, ALT may be tested to make sure they do not have chronic liver disease.

When ALT is used to monitor the treatment of persons who have liver disease, it may be ordered on a regular basis during the course of treatment to determine whether the therapy is effective.

Normally, levels of ALT in the blood are low.

Very high levels of ALT (more than 10 times the highest normal level) are usually due to acute hepatitis, often due to a virus 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 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 the highest normal level. In this case, ALT levels often vary between normal and slightly increased, so doctors typically will order the test 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), 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. There are a few exceptions. The AST/ALT ratio is usually increased in alcoholic hepatitis, cirrhosis, and with muscle injury.

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 doctor about all the drugs and health supplements you are taking. Eating too much fast food can also cause mild increases in ALT by causing liver damage; this typically will return to normal when a normal diet is resumed.