Celiac disease is an autoimmune disorder in genetically predisposed individuals, triggered by ingesting gluten from wheat, barley, and rye. When a person with celiac disease consumes gluten, their immune system attacks the lining of the small intestine. This reaction produces specific antibodies that circulate in the blood. These antibodies are reliable indicators of the disease, making them fundamental to diagnosis and management.
Understanding the Immune Reaction to Gluten
In people with celiac disease, the immune system incorrectly identifies a gluten protein fraction called gliadin as harmful, prompting an inflammatory response. This reaction is concentrated in the intestinal lining, which is covered in small, finger-like projections called villi responsible for absorbing nutrients from food.
The immune system’s attack is directed at both the gluten protein and the body’s own tissues. Immune cells damage the villi, leading them to flatten and become less effective at absorption. This intestinal damage, or villous atrophy, is the source of many symptoms associated with celiac disease.
As part of this response, the body produces several types of autoantibodies. These proteins target specific components involved in the inflammatory cascade and contribute to the ongoing damage to the small intestine.
Primary Antibodies for Celiac Disease Detection
The primary antibody test detects Immunoglobulin A (IgA) antibodies against the enzyme tissue transglutaminase (tTG-IgA). In celiac disease, the immune system targets this enzyme, and the resulting tTG-IgA antibodies are highly sensitive and specific markers. Their levels often correlate with the degree of intestinal damage.
Another specific marker is the endomysial antibody (EMA-IgA). Since EMA antibodies also bind to tissue transglutaminase, the EMA test detects the same autoimmune process. It is often used to confirm a positive tTG-IgA result.
Antibodies to deamidated gliadin peptide (DGP) are also measured as both IgA and Immunoglobulin G (IgG) tests. DGP antibody tests are useful for diagnosing celiac disease in young children, where tTG antibodies may be less reliable, and in individuals with an IgA deficiency.
Because the most sensitive tests detect IgA-class antibodies, total blood IgA levels are also measured. A general IgA deficiency can cause false negative results on tTG-IgA or EMA-IgA tests. If a deficiency is found, diagnosis relies on IgG-based tests like tTG-IgG or DGP-IgG.
The Celiac Antibody Testing Procedure
Diagnosing celiac disease begins with a blood test to measure the levels of specific antibodies like tTG-IgA, EMA-IgA, or DGP. A positive result indicates a high probability of celiac disease.
For antibody testing to be accurate, the individual must be on a regular, gluten-containing diet. Starting a gluten-free diet before testing causes antibody levels to decrease, which can lead to a false negative result. Medical guidelines recommend consuming gluten daily for several weeks before the blood draw to ensure antibodies are detectable.
While a positive antibody test is a strong indicator, a definitive diagnosis has historically required an intestinal biopsy. This procedure involves an endoscopy to collect small tissue samples from the small intestine. A pathologist then examines these samples for the characteristic flattening of the villi.
In some cases, particularly for children with very high tTG-IgA antibody levels, a diagnosis may be made without a biopsy if confirmed with a positive EMA test. This approach avoids an invasive procedure for children with clear serological evidence of the disease. For most adults, a biopsy remains the standard for confirming the diagnosis.
Monitoring Celiac Disease with Antibodies
After a celiac disease diagnosis is confirmed, antibody testing transitions into a method for monitoring the condition. The only treatment is strict, lifelong adherence to a gluten-free diet. Following the removal of gluten, the autoimmune reaction ceases, and the intestinal lining can begin to heal.
Physicians use follow-up antibody tests to verify that the gluten-free diet is effective. After starting the diet, antibody levels are expected to decline significantly over several months, typically normalizing within a year. Regular blood tests, often performed at six and twelve months post-diagnosis and then annually, track this decline. A successful reduction in antibody titers is a good indication that the intestinal villi are regenerating.
Persistently elevated or rising antibody levels after diagnosis are a sign of ongoing exposure to gluten. This exposure can be intentional or, more commonly, accidental, resulting from cross-contamination or hidden gluten in processed foods. Monitoring antibody levels helps healthcare providers and patients identify and address issues with dietary adherence, ensuring long-term management of the disease.