An ALT blood test is a medical test used to diagnose liver disorders. ALT stands for alanine transaminase, which is an enzyme found mostly in the liver. When liver cells are damaged, ALT is released into the blood, and an ALT blood test measures the amount of ALT in the blood. An ALT blood test is often part of a routine blood screening to check the health of the liver, and it may also help diagnose or monitor liver problems.

An ALT blood test is usually done with a group of other liver function tests that check how well the liver is working. These tests may also be ordered if you have symptoms of liver damage, such as nausea, vomiting, or abdominal pain. An ALT blood test is most often included in a blood test panel, such as a liver enzyme panel or a comprehensive metabolic panel.

The normal range for ALT levels in the blood is 4 to 36 U/L. An increased ALT level is often a sign of liver disease, and liver disease is even more likely when the levels of substances checked by other liver blood tests have also increased. An increased ALT level may be due to any of the following:

• Liver disease, such as hepatitis or cirrhosis
• Alcohol abuse
• Heart failure
• Pancreatitis
• Mononucleosis
• Muscle injury
• Certain medications, such as statins

It is important to note that an ALT blood test is not used alone to diagnose liver conditions, as many types of liver problems can cause ALT levels to increase.