If your doctor suspects you or a loved one has celiac disease, the first thing she will likely do is order a gliadin IgA test along with a test for gliadin IgG. Combined, these two tests will give your doctor the information she needs in order to safely diagnose celiac disease.
How Antibodies Work
When you contract a bacterial infection, your body responds by producing antibodies. These antibodies are created from proteins in your body called immunoglobulins, abbreviated as Ig. When bacteria enter your body, the antibodies attack the cause of the infection in order to eliminate it. Unfortunately, that is the same response which occurs when some people eat gluten.
The presence of IgA and IgG anti-gliadin antibodies indicate your body is in attack mode. It is fighting the gluten which it perceives as harmful, causing an inappropriate autoimmune reaction. Both IgA and IgG are found within your intestines, with IgG making up about three-quarters of all the antibodies within you. The antibody present is specific to whatever foreign body is triggering its response.
Gliadin IgA Test
Gliadin is a protein found within gluten. Its presence is what triggers the formation of the IgA and IgB anti-gliadin antibodies. The gliadin IgA test is one tool your doctor uses to find out if you are gluten-intolerant.
The test analyzes the serum of your blood using blood drawn from a vein in your arm. The blood test is virtually painless, though you may develop a small bruise at the site where your blood was drawn. The serum is the plasma portion of your blood minus the clotting proteins. This is where the presence of antibodies is likely to occur. Normal values for IgA are 85-385 milligrams per deciliter,
Testing for IgA anti-gliadin antibodies has a specificity of about 97 percent, which translates into a 97 percent probability that you do indeed have celiac disease. However, the absence of IgA anti-gliadin antibodies is not necessarily a definitive indication that you don't have celiac disease.
A 1989 study published in the European Journal of Pediatrics (148(6):496-502) found that 11 percent of the children with untreated celiac disease did not have these antibodies. So, there is a strong likelihood that the IgA test only may give a false negative, leaving the researchers to avoid recommending it as a celiac disease screen.
Gliadin IgG Test
The solution to developing an accurate screening test requires a way to reduce the number of false negative readings. One way to complement the highly specific results of the gliadin IgA test is to test for the presence of IgG anti-gliadin antibodies as well.
The 1989 study also found that when the two tests are used together, the accuracy of the combined analysis increased dramatically to at least 96 percent sensitivity and a specificity of 97 percent, giving doctors a highly reliable tool in order to diagnose celiac disease.
There are three caveats with using this test as a definitive indication of celiac disease. First, you probably noticed that there is a small percentage which may not be diagnosed. Some individuals just don't produce enough IgA to be considered high and fight gliadin with IgG anti-gliadin antibodies.
Secondly, high levels of IgA can indicate other conditions such as rheumatoid arthritis and systemic lupus erythematosus (SLE), though a thorough examination may easily eliminate other causes. Finally, if you haven't been eating a lot of gluten-containing foods or have gone gluten-free before the test, IgA may not be detected. Blood levels of IgA decline rapidly when gluten is eliminated from your diet, leading to a false negative. Because of these factors, your doctor will want to confirm the results with a biopsy of your small intestine.
Your IgA levels respond quickly to gluten in your diet by rapidly increasing when you eat foods containing gluten. Therefore, another application of the test can be to monitor your levels of IgA anti-antibodies to make sure your body isn't going into an immune response.
Blood tests are a non-invasive tool your doctor can use to provide information regarding the inner-workings of your body. Testing for IgA is one way researchers can continue to explore treatment options and provide hope for celiac disease sufferers.