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 (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
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.
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.
ALT used to be called SGPT, which stands for serum glutamic-pyruvic transaminase. The ALT blood test was formerly known as the SGPT test.
References
- American Liver Foundation. [Internet]. New York: American Liver Foundation; c2022. . Diagnosing Liver Disease – Liver Biopsy and Liver Function Tests; [updated 2020 Feb 17; cited 2022 Feb 16]; [about 3 screens]. Available from: https://liverfoundation.org/for-patients/about-the-liver/diagnosing-liver-disease/
- Hinkle J, Cheever K. Brunner & Suddarth’s Handbook of Laboratory and Diagnostic Tests. 2nd Ed, Kindle. Philadelphia: Wolters Kluwer Health, Lippincott Williams & Wilkins; c2014. Alanine Aminotransferase (ALT); p. 31.
- Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; 2022. Elevated liver enzymes; [cited 2022 Feb 24]; [about 3 screens]. Available from: https://www.mayoclinic.org/symptoms/elevated-liver-enzymes/basics/definition/sym-20050830
- Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c2022. Liver disease; [cited 2022 Feb 24]; [about 8 screens]. Available from: https://www.mayoclinic.org/diseases-conditions/liver-problems/symptoms-causes/syc-20374502
- National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests; [updated 2022 Mar 24; cited 2022 Feb 24]; [about 5 screens]. Available from: https://www.nhlbi.nih.gov/health/blood-tests
- Testing.com [Internet]. Seattle (WA).: OneCare Media; c2022–. Alanine Aminotransferase (ALT); [modified 2021 Nov 9; cited 2022 Feb 24]; [about 14 screens]. Available from: https://www.testing.com/tests/alanine-aminotransferase-alt/
- Testing.com [Internet]. Seattle (WA).: OneCare Media; c2022. Liver Panel; [modified 2021 Nov 9; cited 2022 Feb 24]; [about 13 screens]. Available from: https://www.testing.com/tests/liver-panel/
- University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2022. Health Encyclopedia: ALT; [cited 2022 Feb 24]; [about 4 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=alt_sgpt
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