What It Is
An aspartate aminotransferase (AST) test is often part of an initial screening for liver disease.
The liver plays a variety of important roles in the body: It stores fuel from food, makes proteins, and helps remove toxins from the body. The liver also makes bile, a fluid that helps in digestion. Proteins called enzymes help the liver build and break down proteins. AST (or SGOT, which stands for serum glutamic-oxaloacetic transaminase) is one of these enzymes.
AST is found in many tissues throughout the body, including the liver, heart, muscles, kidney, and brain. If any of these organs or tissues is affected by disease or injury, AST is released into the bloodstream. This means that AST isn't as specific an indicator of liver damage as ALT (also known as alanine aminotransferase, another type of enzyme found almost entirely in the liver).
However, when doctors look at blood levels of AST — especially in relation to the amounts of other liver enzymes — they can get important information about how well the liver is functioning and what type of disease or problem might be affecting it.
Why It's Done
If your child is experiencing symptoms of liver disease — including jaundice (yellowish skin or eyes), dark urine, nausea, vomiting, or abdominal swelling — the AST test may be ordered. It may also be ordered to help diagnose infections of the liver such as viral hepatitis, or to monitor patients taking medications that can cause liver-related side effects.
The AST test is often performed as part of a full hepatic function panel that includes other liver enzyme tests. Looking at AST levels along with those of other liver enzymes — such as ALT and alkaline phosphatase (ALP) — can give doctors more specific information about liver problems.
Preparation
No special preparations are needed for this test. You should tell your doctor about any medications your child is taking because certain drugs might alter the test results.
On the day of the test, having your child wear a short-sleeve shirt can make things faster and easier for the technician who will be drawing the blood.
The Procedure
A health professional will usually draw the blood from a vein. For an infant, the blood may be obtained by puncturing the heel with a small needle (lancet). If the blood is being drawn from a vein, the skin surface is cleaned with antiseptic, and an elastic band (tourniquet) is placed around the upper arm to apply pressure and cause the veins to swell with blood. A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.
After the procedure, the elastic band is removed. Once the blood has been collected, the needle is removed and the area is covered with cotton or a bandage to stop the bleeding. Collecting blood for this test will only take a few minutes.
What to Expect
Either method (heel or vein withdrawal) of collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may be some mild bruising, which should go away in a few days.
Getting the Results
The blood sample will be processed by a machine. The results are usually reported within a few hours or the next day.
If the results seem to point to liver damage or disease, further testing may be necessary to determine what's causing the problem and how to treat it.
Risks
The AST test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn:
- fainting or feeling lightheaded
- hematoma (blood accumulating under the skin causing a lump or bruise)
- pain associated with multiple punctures to locate a vein
Helping Your Child
Having a blood test is relatively painless. Still, many children are afraid of needles. Explaining the test in terms your child can understand might help ease some of the fear.
Allow your child to ask the technician any questions he or she might have. Tell your child to try to relax and stay still during the procedure, as tensing muscles and moving can make it harder and more painful to draw blood. It also may help if your child looks away when the needle is being inserted into the skin.
If You Have Questions
If you have questions about the AST test, speak with your doctor.
Reviewed by: Steven Dowshen, MD
Date reviewed: November 2008
