ALT Blood Test

An ALT test measures the amount of ALT in your blood. This test is commonly used to help diagnose liver damage or disease. ALT (alanine transaminase) is an enzyme, a protein that speeds up certain chemical reactions in your body.

It is found mainly in your liver. Usually, you will have low levels of ALT in your blood. But when liver cells are damaged, they release ALT into the bloodstream.

High levels of ALT in your blood may be a sign of a liver injury or disease. Some types of liver disease cause high ALT levels even before you have symptoms of the disease. So, an ALT blood test may help diagnose certain liver diseases early, when they may be easier to treat.

An ALT test is usually ordered as part of a group of liver function tests.

Why this test is done

Your health care provider may order an ALT blood test as part of a routine checkup. An ALT test is usually done with a group of other liver function tests that check how well your liver is working. Many liver function tests are included in a common blood test called a comprehensive metabolic panel (CMP).

These tests may also be ordered if you have symptoms of liver damage, such as:

• Nausea and vomiting
• Lack of appetite
• Fatigue
• Weakness
• Jaundice, a condition that causes your skin and eyes to turn yellow
• Swelling and/or pain in your abdomen (belly)
• Swelling in your ankles and legs
• Dark-colored urine (pee) and/or light-colored stool (poop)
• Frequent itching

Your provider may also order an ALT blood test if you have a high risk of liver damage because of:

• A family history of liver disease
• Alcohol use disorder (AUD)
• Obesity
• Diabetes
• Taking certain medicines that can cause liver damage
• Hepatitis or exposure to hepatitis

How to prepare

You may need to stop taking certain medicines before the test, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

An ALT test is usually ordered with other blood tests. You usually need to fast (not eat or drink) for several hours before these tests. Your provider will let you know if there are any special instructions.

Sample type

Blood

Other names for this test

Alanine aminotransferase (ALT), Serum Glutamic-Pyruvic Transaminase (SGPT), GPT, Alanine Transaminase