tTG-IgA Test

A tTG-IgA test is a blood test that helps diagnose celiac disease. It works by measuring a certain antibody that your immune system makes when it overreacts to gluten and an enzyme in your body associated with it. The enzyme is called tissue transglutaminase (tTG). Gluten is a protein that’s in many foods, especially wheat, rye and barley. If the blood test shows that you have this antibody (against tTG), your provider may suspect that you have celiac disease.

Healthcare providers use this test for children and adults. It’s usually the first screening test, but providers often combine it with other tests to confirm celiac disease.

Why are tTG-IgA tests done?

Healthcare providers use this test for children and adults with signs and symptoms of celiac disease. It can also be used as a screening test for people with a high risk of celiac disease due to conditions like Type 1 diabetes, autoimmune thyroid disease or a family history of celiac disease.

Common signs and symptoms of celiac disease include:

• Diarrhea
• Constipation
• Bloating
• Abdominal pain
• Growth faltering (typically among children)
• Malnutrition
• Infertility
• Anemia

How does the test work?

A tTG-IgA test is a blood test. Healthcare providers take a sample of blood (usually from a vein in your arm) and then send it to a lab for analysis.

The test looks for antibodies your immune system makes when it overreacts to gluten and an enzyme in your body associated with it. These antibodies show up in your blood. The term "tTG-IgA" stands for tissue transglutaminase IgA.

• Tissue transglutaminase (tTG) is the name of the enzyme.
• IgA stands for immunoglobulin A. This is the antibody your immune system releases, mostly in your small intestine, for fending off microbes.

If you have celiac disease, your immune system is triggered when you eat foods containing gluten. It then makes antibodies that attack tissue transglutaminase by mistake. If you have a positive tTG-IgA test, it means the antibody was found in your blood.

You usually don’t need to do anything to prepare for this test. But you need to make sure you’re still eating gluten. You can’t have this test if you’ve already eliminated gluten from your diet because the results won’t be accurate.

Your provider will let you know the results and what comes next. It could take up to five days to receive results.

What are the risks of a transglutaminase IgA test?

The test is low-risk. It involves giving a blood sample. You may bruise or have pain from the needle in your arm.

If problems occur, they usually involve false results. False negatives could happen if you have low IgA levels already. This can occur if you have IgA deficiency, which is a genetic condition.

You also must take this test while you’re still eating gluten. If you’ve already gone gluten-free, the results won’t be accurate.

There are limitations to this test, too. A positive result means celiac disease is likely. But it’s not 100%, which means you’ll still need more tests.

What is the normal range for tissue transglutaminase IgA?

High tTg-IgA levels usually point to celiac disease. But your provider will usually confirm the diagnosis with other tests like a biopsy of your small intestine.

The normal ranges are as follows:

• Negative (normal) result: Less than 4 U/mL
• Borderline result: 4–10 U/mL
• Positive result: Greater than 10 U/mL

Your healthcare provider will let you know what your results mean for you (or for your child). A tissue transglutaminase IgA test is just one step in the process of reaching a diagnosis.

How accurate is the test?

The tTG-IgA test is very accurate as long as you’re still eating gluten. It finds celiac disease in virtually all individuals, as long as they haven’t started eating a gluten-free diet.

When should I call my doctor?

Contact a healthcare provider if you or your child have symptoms of gluten intolerance. They may recommend a tissue transglutaminase IgA blood test. Gluten intolerance may also be due to other reasons, such as gluten sensitivity.