Coeliac serology tests are blood tests used to help diagnose celiac disease, an autoimmune condition where ingestion of gluten (a protein found in wheat, barley, and rye) leads to damage in the small intestine. These tests look for specific antibodies in the blood that are often elevated in individuals with celiac disease. The presence of these antibodies indicates an immune response to gluten.
Here are the primary coeliac serology tests:
- Anti-Tissue Transglutaminase Antibodies (tTG-IgA):
- This is the most commonly used serologic test for celiac disease.
- tTG is an enzyme in the body, and in people with celiac disease, the immune system mistakenly produces antibodies against this enzyme in response to gluten ingestion.
- The tTG-IgA test is quite specific for celiac disease, meaning that if it’s positive, there’s a high likelihood of the disease. However, some other conditions may occasionally produce a positive result, so it’s essential to interpret this in the context of the clinical picture.
- Endomysial Antibodies (EMA-IgA):
- This test detects antibodies against the endomysium, a part of the tissue surrounding muscle fibers.
- The EMA-IgA test is highly specific for celiac disease but is used less frequently than tTG-IgA due to higher costs and being more labor-intensive.
- Deamidated Gliadin Peptide Antibodies (DGP-IgA and DGP-IgG):
- Gliadin is a component of gluten, and in the process of celiac disease, it can be altered (or “deamidated”) in the intestines. The immune system then produces antibodies against this altered gliadin.
- DGP tests can be useful in situations where tTG and EMA tests are not conclusive, especially in young children.
- Total Serum IgA:
- This is not a test for celiac disease per se but is often done alongside the other tests.
- Some people have selective IgA deficiency, meaning they produce very low levels of IgA antibodies. This can lead to false-negative results on the tTG-IgA and EMA-IgA tests.
- By checking total serum IgA, clinicians can determine if a patient has this deficiency and interpret the other test results accordingly.
If serologic tests suggest celiac disease, the diagnosis is usually confirmed with a biopsy of the small intestine, taken via endoscopy. This biopsy will show characteristic changes of the intestinal lining in people with celiac disease, such as villous atrophy.
It’s also important to note that these serologic tests are most accurate when the person is on a gluten-containing diet. If someone has already started a gluten-free diet, the test results might not be conclusive.