A tissue transglutaminase IgA and/or IgG test is used as part of an evaluation for certain autoimmune conditions, most notably celiac disease.
An autoimmune disease can occur when the body's immune system mistakenly perceives a nonthreatening substance — in the case of people with celiac disease, gluten, a protein found in wheat, barley, rye, and oats — as a foreign invader and attacks it. This immune system response in celiac disease also involves the production of antibodies directed against an enzyme normally present in the intestines called tissue transglutaminase (tTG).
In celiac disease, the body produces two types of antibodies that attack tTG: immunoglobulin A (IgA) and immunoglobulin G (IgG). Measuring the IgA form of tTG antibody in the blood is more useful in detecting celiac disease because it's made in the small intestine, where gluten causes inflammation and irritation in sensitive people.
Levels of the IgG form of tTG antibody, on the other hand, are less specific to celiac disease, but may still be useful in diagnosing the condition in people who are unable to make normal amounts of IgA antibodies.
Why It's Done
The tTG IgA or IgG antibody tests are usually done to help doctors diagnose celiac disease.
For accurate results, your child must currently be eating a diet that includes gluten-containing foods, such as breads, pastas, and baked goods. The body will only produce antibodies when it's exposed to gluten. If gluten has been removed from the diet, there won't be an antibody response to measure.
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 A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.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.
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. Results are commonly available within a day or two. If results suggest celiac disease, the doctor will likely perform further tests, including a biopsy of the small intestine to look for evidence of gluten-induced inflammation.
This 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 tTG IgA or IgG tests, speak with your doctor. You can also talk to the technician before the procedure.