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
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.
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:
Slightly high levels of AST may be caused by:
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 (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.
Credits
| By | Healthwise Staff |
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| Primary Medical Reviewer | Kathleen Romito, MD - Family Medicine |
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| Specialist Medical Reviewer | Peter J. Kahrilas, MD - Gastroenterology |
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| Last Revised | February 17, 2010 |
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