What is an ALT Blood Test? 

ALT stands for alanine transaminase. It is an enzyme found mostly in the liver. An ALT test measures the amount of ALT in the blood.

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 before you have symptoms of the disease. So, an ALT blood test may help diagnose certain liver diseases early.

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

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. 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 for liver damage because of:

  • A family history of liver disease
  • Alcohol abuse 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 don’t need any special preparations for an ALT blood test. But 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 to follow.

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 to decide if you need other tests to make a diagnosis.

In general, high levels of ALT may be a sign of liver damage from hepatitis, infection, cirrhosis, liver cancer, or other liver diseases. The damage may also be from a lack of blood flow to the liver or certain medicines or 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, certain medicines and dietary supplements, intense exercise, how much you weigh, and having a menstrual period.

To learn what your results mean, talk with your provider. And be sure tell your provider about all the medicines and supplements you take.