Alanine Aminotransferase (ALT)

Test Overview

An alanine aminotransferase (ALT) test measures the amount of this enzyme in the blood. ALT is found mainly in the liver, but also in smaller amounts in the kidneys, heart, muscles, and pancreas. ALT was formerly called serum glutamic pyruvic transaminase (SGPT).

ALT is measured to see if the liver is damaged or diseased. Low levels of ALT are normally found in the blood. But when the liver is damaged or diseased, it releases ALT into the bloodstream, which makes ALT levels go up. Most increases in ALT levels are caused by liver damage.

The ALT test is often done along with other tests that check for liver damage, including aspartate aminotransferase (AST), alkaline phosphatase, lactate dehydrogenase (LDH), and bilirubin. Both ALT and AST levels are reliable tests for liver damage.

Why It Is Done

The alanine aminotransferase (ALT) test is done to:

  • Identify liver disease, especially cirrhosis and hepatitis caused by alcohol, drugs, or viruses.
  • Help check for liver damage.
  • Find out whether jaundice was caused by a blood disorder or liver disease.
  • Keep track of the effects of cholesterol-lowering medicines and other medicines that can damage the liver.

How To Prepare

Avoid strenuous exercise just before having an ALT test.

Tell your doctor if you:

  • Are taking any medicines. Many medicines can interfere with test results. Your doctor may instruct you to stop taking certain medicines for several days before having an ALT test. Some herbs and natural products (such as echinacea and valerian) also can affect ALT results.
  • Are allergic to any medicines.
  • Are or might be pregnant.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean. To help you understand the importance of this test, fill out the medical test information formmedical test information form(What is a PDF document?).

How It Is Done

The health professional taking a sample of your blood will:

  • Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Put a gauze pad or cotton ball over the needle site as the needle is removed.
  • Put pressure on the site and then put on a bandage.

How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

There is very little chance of a problem from having blood sample taken from a vein.

  • You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
  • Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicines, tell your doctor before your blood sample is taken.

Results

An alanine aminotransferase (ALT) test measures the amount of this enzyme in the blood. Results are usually available within 12 hours.

Normal

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Alanine aminotransferase1

Males:

10–40 units per liter (U/L) or 0.17–0.68 microkats per liter (mckat/L)

Females:

7–35 U/L or 0.12–0.60 mckat/L

High values

High levels of ALT may be caused by:

  • Liver damage from conditions such as hepatitis or cirrhosis.
  • Lead poisoning.
  • Exposure to carbon tetrachloride.
  • Decay of a large tumor (necrosis).
  • Many medicines, such as statins, antibiotics, chemotherapy, aspirin, narcotics, and barbiturates.
  • Mononucleosis.
  • Growth spurts, especially in young children. Rapid growth can cause mildly elevated levels of ALT.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Taking medicines. Talk with your doctor about all the prescription and nonprescription medicines you are taking. You may be instructed to stop taking your medicines for several days before the test.
  • Taking some herbs and natural products, such as echinacea and valerian.
  • Strenuous exercise, injury to a muscle, or injections into a muscle.
  • Recent cardiac catheterization or surgery.

What To Think About

  • The alanine aminotransferase (ALT) value is often used along with the results of the aspartate aminotransferase (AST) test to obtain the AST to ALT ratio. This value can often help determine whether there is damage to the liver related to alcohol abuse. For more information, see the topic Aspartate Aminotransferase (AST).
  • In children with acute lymphocytic leukemia (ALL), very high ALT levels may mean that the disease is likely to progress rapidly.
  • Many different conditions can raise ALT blood levels, so other testing is usually needed to interpret an abnormal ALT result.

References

Citations

  1. Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
  • Handbook of Diagnostic Tests (2003). 3rd ed. Philadelphia: Lippincott Williams and Wilkins.
  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.

Credits

By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Specialist Medical Reviewer Jerome B. Simon, MD, FRCPC, FACP - Gastroenterology
Last Revised November 4, 2011

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