Aspartate Aminotransferase (AST)

Test Overview

An aspartate aminotransferase (AST) test measures the amount of this enzyme in the blood. AST is normally found in red blood cells, liver, heart, muscle tissue, pancreas, and kidneys. AST formerly was called serum glutamic oxaloacetic transaminase (SGOT).

Low levels of AST are normally found in the blood. When body tissue or an organ such as the heart or liver is diseased or damaged, additional AST is released into the bloodstream. The amount of AST in the blood is directly related to the extent of the tissue damage. After severe damage, AST levels rise in 6 to 10 hours and remain high for about 4 days.

The AST test may be done at the same time as a test for alanine aminotransferase, or ALT. The ratio of AST to ALT sometimes can help determine whether the liver or another organ has been damaged. Both ALT and AST levels can test for liver damage.

Why It Is Done

An aspartate aminotransferase (AST) test is done to:

• Check for liver damage.
• Help identify liver disease, especially hepatitis and cirrhosis. Liver disease may produce symptoms such as pain in the upper abdomen, nausea, vomiting, and sometimes jaundice.
• Check on the success of treatment for liver disease.
• 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

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 AST test. Some herbs and natural products (such as Echinacea and valerian) also can affect AST 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 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 medicine, tell your doctor before your blood sample is taken.

Results

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

Normal

Normal values can vary widely from lab to lab.

High values

Very high levels of AST may be caused by:

• Recent or severe liver damage, such as hepatitis caused by a viral infection or drug reaction.
• Decay of a large tumor (necrosis).
• Shock.

Moderately high levels of AST may be caused by:

• Long-term (chronic) diseases that affect the liver, such as cirrhosis.
• A heart attack or heart failure.
• Alcohol abuse.
• Having taken high doses of vitamin A.
• Kidney or lung damage.
• Mononucleosis.
• Duchenne muscular dystrophy.
• Some types of cancer.
• A rare autoimmune disease that affects muscles (myositis).

Slightly high levels of AST may be caused by:

• Fatty deposits in the liver.
• Alcohol abuse.
• An overdose of acetaminophen (Tylenol). People who drink alcohol and take a lot of acetaminophen (such as Tylenol) can also have high AST blood levels.
• Many medicines, such as statins, antibiotics, chemotherapy, aspirin, narcotics, and barbiturates.

AST levels may be high when a disease first develops, which is often when tissue damage is most severe. Decreasing levels of AST in the blood may be a sign of recovery from the disease or injury.

Many other conditions, including severe burns, traumatic injuries, pulmonary embolism, or heat exhaustion and heatstroke, and ingestion of poisonous mushrooms may cause elevated AST levels.

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 large doses of vitamin A.
• Taking some herbs and natural products, such as Echinacea and valerian.
• Injury to a muscle.
• Recent cardiac catheterization or surgery.

What To Think About

• The aspartate aminotransferase (AST) test is more effective than the alanine aminotransferase (ALT) test for detecting liver damage caused by alcohol abuse. The AST to ALT ratio may sometimes help determine if liver damage is related to alcohol dependence. For more information, see the medical test Alanine Aminotransferase (ALT).
• Many different conditions can raise AST blood levels, so other testing is usually needed to interpret an abnormal AST result.

References

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.
• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.

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