What is an 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.

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

What is it used for?

An ALT blood test is often part of a routine blood screening to check the health of your liver. The test may also help diagnose or monitor liver problems.

Why do I need an ALT blood test?

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

What happens during an ALT blood test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

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.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

An ALT blood test is often done as part of a group of liver function tests. Liver function tests measure several different proteins, substances, and enzymes that show how well your liver is working. Your provider usually compares your ALT results with the results of the other liver tests to evaluate your liver health and decide if you need other tests to make a diagnosis.

Lower-than-usual levels of ALT in your blood are not common. Your provider may do more tests since this may be a sign of:

• B6 deficiency
• Chronic kidney disease

Higher-than-usual levels of ALT in your blood may be a sign of liver damage from:

• Hepatitis
• Infection
• Cirrhosis
• Liver cancer
• Other liver diseases
• A lack of blood flow to the liver
• Certain medicines, such as cholesterol or pain medicines
• Poisons

If your results show you have a high level of ALT, it doesn't always mean that you have a medical condition that needs treatment. Many things can affect your results, such as your age, sex, weight, and certain medicines and dietary supplements. Your ALT levels can also be affected by intense exercise and where you are in your menstrual cycle.

To learn what your results mean, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about an ALT blood test?

ALT test results may help tell the difference between damage from acute (sudden) liver problems and chronic (long-term) liver problems. But the amount of ALT in your blood isn't related to how much your liver may be damaged.

Your ALT is usually measured along with another liver enzyme called AST as part of a liver function panel. Since ALT is mostly found in the liver, an ALT test checks more specifically for liver damage.