tTG IgA Test

Tissue transglutaminase IgA (tTG-IgA) is a type of antibody, a protein made by your immune system, that targets your own body by mistake when you have celiac disease. Celiac disease is an autoimmune disorder where eating gluten (a protein found in wheat, barley, and rye) triggers inflammation and damage in the small intestine. This damage prevents your body from properly absorbing nutrients, leading to symptoms like diarrhea, bloating, anemia, and even osteoporosis over time.

In healthy individuals, tissue transglutaminase (an enzyme found in many tissues) plays a role in repairing cells. In celiac disease, the immune system wrongly identifies this enzyme as harmful after gluten is eaten and produces tTG-IgA antibodies to attack it. The production of these antibodies is a key part of the immune cascade that leads to the intestinal damage seen in celiac disease.

When figuring out if you have celiac disease, you often start by measuring tTG-IgA levels in the blood. This test is highly sensitive and specific, meaning that it correctly identifies most people who have celiac disease and correctly excludes those who do not. A strongly positive tTG-IgA (particularly if it is more than 10 times the normal limit) is so accurate that, in some adults, it can allow a diagnosis without needing a biopsy of the small intestine.

However, the story is not always straightforward. Some factors can affect tTG-IgA results:

• IgA Deficiency: About 2-5% of people with celiac disease do not produce enough IgA, which can cause a false negative result. In these cases, doctors use other tests based on a different antibody class, called IgG.
• Gluten-Free Diets: If someone has already started avoiding gluten before testing, tTG-IgA levels can drop and become falsely negative. Testing is most accurate when gluten is still being eaten regularly.
• Other Diseases: Rarely, tTG-IgA can be elevated in conditions unrelated to celiac disease, such as severe heart failure or chronic liver disease, so context and clinical evaluation are important.

Once diagnosed, tTG-IgA can also be used to monitor how well someone is sticking to a gluten-free diet. Over time, if the diet is strict and effective, antibody levels typically fall back to normal.