ALT (Alanine Aminotransferase) Test
What Is an Alanine Aminotransferease (ALT) Test?
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 kidneys and other organs, too.
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.
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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). 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 ALT-to-AST 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
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.
Show Sources
American Association for Clinical Chemistry: “ALT.”
Mayo Clinic: “Liver Disease: Definition.” “Liver function tests.”
Medscape: “Alanine Aminotransferase.”
National Heart, Lung, and Blood Institute: “What To Expect With Blood Tests.”
Nemours Foundation: “Blood Test: Alanine Aminotransferase (ALT, or SGPT).”
University of Rochester Medical Center: “ALT.”
ALT (Alanine Aminotransferase) Test
An alanine aminotransferase (ALT) test measures the level of the enzyme ALT in your blood. This test can help doctors evaluate liver function or determine the underlying cause of a liver problem.
ALT is an enzyme that is found mostly in the liver. The liver is the body’s largest gland. It has several important functions, including:
- making proteins
- storing vitamins and iron
- removing toxins from your blood
- producing bile, which aids in digestion
Proteins called enzymes help the liver break down other proteins so your body can absorb them more easily. ALT is one of these enzymes. It plays a crucial role in metabolism, turning food into energy. The ALT test is often part of an initial screening for liver disease.
ALT is normally found inside liver cells. However, when your liver is damaged or inflamed, ALT can be released into your bloodstream. This causes serum ALT levels to rise.
An increase in ALT is often the first sign of a liver problem, and ALT is often elevated before other symptoms appear.
An ALT test is also known as a serum glutamic-pyruvic transaminase (SGPT) test or an alanine transaminase test.
The ALT test is usually used to determine whether someone has liver injury or failure. Your doctor may order an ALT test if you’re having symptoms of liver disease, including:
- jaundice, which is yellowing of your eyes or skin
- dark urine
- nausea
- vomiting
- pain in the right upper quadrant of your abdomen
Liver damage generally causes an increase in ALT levels. The ALT test can evaluate the levels of ALT in your bloodstream, but it can’t show how much liver damage there is or how much fibrosis, or scarring, is present.
The test also can’t predict how severe the liver damage will become.
An ALT test is often done with other liver enzyme tests. Checking ALT levels along with levels of other liver enzymes can provide your doctor with more specific information about a liver problem.
An ALT test may be part of a routine checkup or requested if someone has risk factors for liver disease, including:
- family history
- heavy alcohol use
- exposure to hepatitis
- taking certain medications
- diabetes
Other reasons to perform an ALT test include:
- monitoring the progression of liver diseases, such as hepatitis or liver failure
- assessing whether treatment for liver disease should be started
- evaluating how well treatment is working
An ALT test doesn’t require any special preparation. However, you should tell your doctor about any prescription or over-the-counter medications you’re taking. Some medications may affect the levels of ALT in your blood.
Your doctor might tell you to avoid taking certain medications for a period of time before the test.
An ALT test involves taking a small sample of blood, as outlined here:
- A healthcare professional uses an antiseptic to clean your skin in the area where they will take the sample.
- They will tie an elastic band around your upper arm, which stops the flow of blood and makes the veins in your arm more visible.
- Once they find a vein, they will insert a needle. This may cause a brief pinching or stinging sensation. The blood is drawn into a tube attached to the end of the needle. In some cases, more than one tube may be required.
- After enough blood has been collected, the healthcare professional removes the elastic band and the needle. They place a piece of cotton or gauze over the puncture site and cover that with a bandage or tape to keep it in place.
- The blood sample is sent to a laboratory for analysis.
- The laboratory sends the test results to your doctor. Your doctor may schedule an appointment with you to explain the results in more detail.
An ALT is a simple blood test with few risks. Bruising can sometimes occur in the area where the needle was inserted. The risk of bruising can be minimized by applying pressure to the injection site for several minutes after the needle is removed.
In very rare cases, the following complications can occur during or after an ALT test:
- excessive bleeding where the needle was inserted
- an accumulation of blood beneath your skin, which is called a hematoma
- lightheadedness or fainting at the sight of blood
- an infection at the puncture site
Normal results
According to the American College of Gastroenterology, the normal value for ALT in blood for people without risk factors for liver disease ranges from 29 to 33 international units per liter (IU/L) for males and 19 to 25 IU/L for females. This value can vary depending on the lab.
This range can be affected by certain factors, including sex and age. It’s important to discuss your specific results with your doctor.
Abnormal results
Higher-than-normal levels of ALT can indicate liver damage. Increased levels of ALT may be a result of:
- hepatitis, which is an inflammatory condition of the liver
- cirrhosis, which is severe scarring of the liver
- death of liver tissue
- a tumor or cancer in the liver
- a lack of blood flow to the liver
- hemochromatosis, which is a disorder that causes iron to build up in the body
- mononucleosis, which is an infection usually caused by the Epstein-Barr virus
- diabetes
Most lower ALT results indicate a healthy liver. However, studies have shown that lower-than-normal results have been related to increased long-term mortality. Discuss your numbers specifically with your doctor if you’re concerned about a low reading.
If your test results indicate liver damage or disease, you may need more testing to determine the underlying cause of the problem and the best way to treat it.
Last medically reviewed on June 7, 2021
