The alanine aminotransferase (ALT) test is a blood test that checks for liver damage. Your doctor can use this test to find out if a disease, drug, or injury has damaged your liver.
Your liver does a lot of important things for you:
- It makes a fluid called bile that helps your body digest food.
- It removes waste products and other toxins from your blood.
- It produces proteins and cholesterol.
Diseases such as hepatitis and cirrhosis can damage your liver and prevent it from doing its many jobs.
Why Is ALT Important?
This enzyme is found mainly in your liver. Smaller amounts of ALT are in your muscle, kidneys , and other organs.
Your body uses ALT to break down food into energy. Normally, ALT levels in the blood are low. If your liver is damaged, it will release more ALT into your blood and levels will rise. (ALT used to be called serum glutamic-pyruvic transaminase, or SGPT).
Doctors often give the ALT test along with other liver tests.
Why Would My Doctor Order This Test?
Your doctor might recommend ALT if you have symptoms of liver disease or damage, such as:
- Stomach pain or swelling
- Nausea
- Vomiting
- Yellow skin or eyes (a condition called jaundice)
- Weakness
- Extreme tiredness (fatigue)
- Dark-colored urine
- Light-colored poop
- Itchy skin
Here are some reasons you might get this test:
- You've been exposed to the hepatitis virus.
- You drink a lot of alcohol.
- You have a family history of liver disease.
- You take medicine that's known to cause liver damage.
The ALT test can be done as part of a blood panel during a regular exam. If you've already been diagnosed with liver disease, your doctor can use the ALT test to see how well your treatment is working.
How Do I Prepare?
You don't need any special preparation for the ALT test. Your doctor might ask you to stop eating or drinking a few hours before the test.
Tell your doctor what prescription drugs or supplements you take. Some medicines can affect the results of this test.
What Happens During the Test?
A nurse or lab tech will take a sample of your blood, usually from a vein in your arm. They will first tie a band around the upper part of your arm to make your vein fill with blood and swell up. Then they will clean the area with an antiseptic and place a needle into your vein. Your blood will collect into a vial or tube.
The blood test should take only a couple of minutes. After your blood is taken, the lab tech will remove the needle and band, then put a piece of gauze and a bandage over the spot the needle went in to stop the bleeding.
What Are the Risks?
The ALT blood test is safe. Risks are usually minor, and can include:
- Bleeding
- Bruising
- Infection
- Slight pain when the needle is inserted
- Fainting or feeling dizzy
What Do the Results Mean?
You should get your results in about a day. A normal ALT test result can range from 7 to 55 units per liter (U/L), but it varies depending on the laboratory used. Levels are normally higher in men.
Slightly high ALT levels may be caused by:
- Alcohol abuse
- Cirrhosis (long-term damage and scarring of the liver)
- Mononucleosis
- Drugs such as statins, aspirin, and some sleep aids
Moderately high ALT levels may be because of:
- Chronic (ongoing) liver disease
- Alcohol abuse
- Cirrhosis
- Blockage of the bile ducts
- Heart attack or heart failure (when your heart can’t pump enough blood to your body)
- Kidney damage
- Muscle injury
- Damage to red blood cells
- Heat stroke
- Too much vitamin A
Very high ALT levels can be caused by:
- Acute viral hepatitis
- An overdose of drugs such as acetaminophen (Tylenol)
- Liver cancer
- Sepsis
What Other Tests Will I Take?
ALT usually is done as part of a group of liver function tests called a liver panel.
This panel also includes an aspartate aminotransferase (AST) test. AST is another liver enzyme. As with ALT, the levels of AST in your blood rise if your liver is damaged.
Comparing ALT with AST levels gives your doctor more information about the health of your liver. The AST-to-ASL ratio can help your doctor figure out how severe the liver damage is and what might have caused it.
To find out what type of liver disease you have, your doctor might also test the levels of other enzymes and proteins found in your liver, including:
- Albumin
- Alkaline phosphatase
- Bilirubin
- Lactate dehydrogenase (LDH)
- Total protein
- GGT
Talk to your doctor to make sure you understand all of your liver test results. Also find out how these results might affect your treatment.