Antigliadin antibodies are specific immune system proteins that react to components of dietary gluten. These antibodies are formed when the body’s immune system identifies gliadin, a protein found in wheat and other grains, as a foreign substance. Their presence in the bloodstream can indicate an immune response to gluten.
Understanding Antigliadin Antibodies
Gliadin is a protein component of gluten, which is primarily found in wheat, barley, and rye. Gluten itself is a complex mixture of proteins, and gliadin contributes to its elasticity and chewiness. When the body encounters gliadin, the immune system may produce antibodies to target it.
Antibodies are proteins produced by the immune system to identify and neutralize foreign invaders like bacteria and viruses. Antigliadin antibodies (AGA) are a type of antibody generated in response to gliadin. There are two main classes of antigliadin antibodies typically measured: immunoglobulin A (IgA) and immunoglobulin G (IgG). These different classes reflect distinct aspects of the immune response to gliadin.
The IgA class of antigliadin antibodies is often associated with mucosal immunity, as IgA is the primary antibody found in mucous membranes, including those lining the gut. The IgG class of antigliadin antibodies also indicates an immune reaction to gliadin.
Purpose of Antigliadin Antibody Testing
Antigliadin antibody tests were historically used as serological markers for identifying gluten-related disorders. The tests were primarily employed in screening for conditions where the immune system reacts abnormally to gluten, such as celiac disease.
The test aimed to identify an immune reaction to gluten, which could suggest underlying conditions like celiac disease or, in some instances, non-celiac gluten sensitivity. For accurate results, a patient typically needed to be consuming a gluten-containing diet before the test, as gluten exposure is necessary for the body to produce these antibodies.
Interpreting Antigliadin Test Results
When antigliadin antibody test results are positive or elevated, it suggests that the individual’s immune system is producing antibodies in response to gliadin. Such results generally prompt further investigation to determine the specific cause of the immune response.
A negative or normal antigliadin antibody result suggests that the body is not reacting strongly to gliadin. This might occur if a person is consuming little or no gluten, or if their immune system does not identify gliadin as a threat. While negative results make gluten-related disorders less likely, they do not completely rule out such conditions. All test results, whether positive or negative, must be interpreted by a healthcare professional in the context of a patient’s symptoms, medical history, and other diagnostic findings.
Limitations and Current Role of Antigliadin Testing
Antigliadin antibody (AGA) tests have limitations, including lower diagnostic accuracy compared to newer serological markers for celiac disease. Their sensitivity and specificity were about 85%, which means they could produce false positive or false negative results. Due to these limitations, AGA tests are no longer routinely recommended as primary diagnostic tools for celiac disease.
More modern and accurate tests have largely replaced AGA for diagnosing celiac disease. These include anti-tissue transglutaminase (tTG) antibodies, specifically tTG-IgA, which has a sensitivity and specificity of 95% or higher in individuals over two years old. Additionally, anti-endomysial antibodies (EMA) and deamidated gliadin peptide (DGP) antibodies (IgA and IgG) offer improved diagnostic performance.
Despite being largely outdated for celiac disease diagnosis, antigliadin antibody tests may still have a specific, though limited, role. In cases of selective IgA deficiency, where IgA-based tests like tTG-IgA might yield false negative results, IgG-based tests for deamidated gliadin peptides (DGP-IgG) or tTG-IgG are used. AGA tests might also be considered in certain situations, such as in very young children or for investigating suspected gluten-related neurological disorders.