A gamma-glutamyl transpeptidase (GGT) test measures the levels of this enzyme in the blood. GGT is produced in many body tissues, with particularly high concentrations in the liver and gallbladder.
The liver stores fuel from food, makes proteins, helps remove poisons and toxins, and produces bile, a digestive fluid that helps the body absorb fat. The gallbladder stores bile until it's needed.
Why It's Done
Testing for GGT helps doctors evaluate diseases of the liver, gallbladder, and bile ducts (tubes that carry bile from the liver to the gallbladder and intestine). It also can be used to check for liver damage related to ingestion of toxic substances or alcohol abuse.
No special preparations are needed for this test. However, certain drugs might alter the test results, so tell your doctor about any medications your child is taking.
On the day of the test, having your child wear a T-shirt or short-sleeved shirt can make things easier for the technician drawing the blood.
A health professional will usually draw the blood for the test 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 A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.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.
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 day or so.
Getting the Results
The blood sample will be processed by a machine. The results are commonly available after a few hours or the next day.
Although an elevated GGT level may indicate a problem with the liver or gallbladder, this result alone can't enable doctors to identify the specific problem or disease. In the case of an abnormal result, further testing may be necessary.
The GGT test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn. These include:
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 GGT test, speak with your doctor. You can also talk to the technician before the procedure.