<<Disclaimer: Verify this information before applying it to your situation.>> Celiac Blood Tests ------------------ by Dr. Thomas Alexander summarized by Jim Lyles Dr. Thomas Alexander, a gastroenterologist out of Beaumont Hospital and our group's physician advisor, spoke at our April meeting. What follows are some highlights of his talk. Antibodies are proteins that the body makes to kill foreign invaders (viruses, bacteria, etc.) One of the first antibodies found that could be used to diagnose CD was the antigliadin antibody. Gliadin is the part of gluten that seems to cause the problem for celiacs. There are two kinds of antigliadin antibodies: IgA and IgG. Tests for these two antibodies will pick up about 90% of the patients with untreated CD. Once you start a GF diet, these antibodies start to come back down to normal. The IgA antibodies will usually drop back to normal within a few of months; the IgG antibodies may come down to normal within several months to a few years, and in some cases may stay up indefinitely. That does not mean that you still have active CD (although in some cases these blood tests are used to monitor compliance to the GF diet). The antiendomysial antibody test is also about 90% accurate. It is more accurate in cases of people with more severe disease. Celiacs who have only minor changes on their biopsies will often have negative antiendomysial test results. It is also a bit more specific then the antigliadin test. A "sensitive" test is very likely to pick up cases of the disease it is screening for, and very unlikely to miss cases. A "specific" test is very unlikely to be positive for any disease other than the one be screened. It turns out that the antiendomysial and antigliadin tests are not specific to CD; there are other conditions that can yield positive test results. One of these is dermatitis herpetiformis (DH). It turns out that about 90% of the DH patients either have CD or will develop it. These tests can also come back positive for a number of conditions that are not related to CD. There is a third test called the antireticulin antibody test. It is a little more specific than the antigliadin test, but is not as sensitive so it is going to miss a lot of cases. A physician may order only one of these tests, but generally we just order all three of them. These are helpful during the course of the diagnosis; they help determine whether or not to proceed with a gastroscopy or biopsy. These tests can also be useful as corroborative evidence in a patient with an intestinal biopsy consistent with CD. Some doctors also routinely repeat the tests on annual basis. Dr. Alexander does not routinely repeat the tests; he'll order it when he sees some symptoms that make him suspicious of active CD. A third way to use the antibody tests is to screen relatives of a diagnosed celiac for CD. Somewhere between 2-10% (perhaps as many as 15%) of the people who have CD also have a first-degree relative with CD. So it makes sense to screen the first degree relatives (the parents, siblings, and children of the celiac patient) for CD. Once you get beyond the first degree relatives, it is not generally necessary to screen for CD unless, of course, there are symptoms consistent with CD. The other type of blood test to talk about is genetic testing. This is an area that has been evolving rapidly over the last few years. One of the problems in this area is the nomenclature has changed so that articles written five years ago use different terms than reports written today. The body has to identify foreign particles (bacteria, viruses, etc.) and distinguish them from itself. It does this through a series of proteins that have certain configurations that will "fit" to certain foreign molecules. It is similar to a child's toy, a box with a set of differently shaped holes; the idea is to have the child put the correctly shaped object in each hole. The body is genetically programmed to make these "holes". When a foreign particle floats along and happens to fall into a matching hole, it sets off a complex series of interactions that sets off the inflammatory process to kill off this foreign invader. This is determined through a class of proteins called the "Human Lymphocyte Antigen (HLA)" system. There are different classes of this system, classes I, II, and III. The proteins that fit the class I antigens are present in virtually all the cells in the body. The class II antigens are the ones that are involved with CD. Of these there are two, DQB1*0201 and DQA1*0501 that encod e the DQ2 protein. These are present in about 95% of celiacs. The other 5% have antigens that encode the DQ8 protein. One or the other of these genetic "markers" are present in nearly all celiacs. The HLA tests can be used to determine if you have the genetic markers that are consistent with CD. That does not mean you will get CD. Even in identical twins, if one twin has CD only about 75% of the time will the other have CD, so there are obviously environmental factors involved as well as genetics. About 30% of HLA-matched siblings of a celiac will have CD. Latent CD is another topic of interest. This is CD that is "not really here yet" or doesn't show up on a biopsy. This is another area of research that is still evolving. There are different definitions of latent CD. It may be characterized by positive antibody test but negative biopsies. In these patients it is possible that five years down the road repeat biopsies would then be positive and the disease would no longer be latent. It could be that antibody levels become elevated before damage to the small intestinal villi occurs.