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Celiac.com 12/08/2020 - Are you confused about genetic testing for celiac disease? Do you want to know what tests you should request and which laboratory to use? Have you already had celiac DQ genetic testing but are not sure what the results mean or what your risk is of developing celiac disease or gluten sensitivity? These are the questions I will answer in the next few pages. What is HLA DQ celiac genetic testing? To understand celiac DQ genetics and the risk estimates you must also understand how the DQ types are determined and some basic terminology. Each of us has 46 chromosomes, 23 pairs received from our parents. We all have two copies of chromosome 6, one from each parent. Homozygous is when a person has two copies of the same gene, one from each parent. Our white blood cells (leukocytes) have proteins called human leukocyte antigens or HLA proteins that are inherited from our parents. The genetic code that determines our HLA patterns resides on chromosome 6. We all have two DQ patterns, one from each of parents, such that we are all DQx/DQx, where x is a number between 1 and 9. I am DQ2/DQ7 and my wife is DQ2/DQ5. We are both therefore heterozygous for DQ2. That is, we have only one copy of DQ2. Scott Adams, the founder of celiac.com is DQ8/DQ8. He is homozygous for DQ8. There are several HLA patterns. Some are proteins that reside within cells and others are on the outer surface of cells, and are called class II. The class II HLA proteins have very important immune functions. There are several class II HLA protein types but DQ have been found to be important in celiac disease, specifically DQ2 and DQ8. What does it mean to be homozygous or heterozygous for celiac genes? Homozygous means that you have two copies e.g. DQ2/DQ2, DQ8/DQ8 whereas heterozygous means you have one copy of DQ2 or DQ8. Some people have one copy of DQ2 and one of DQ8 (DQ2/DQ8) and they have a greater risk for celiac disease than someone with only one copy of either DQ2 or DQ8 but not as great a risk as someone with two copies of DQ2 (DQ2/DQ2). Since DQ2 is associated with a greater risk of celiac disease than DQ8, then one copy of DQ2 plus a DQ8 (DQ2/DQ8) indicates a higher risk than having two copies of DQ8 (DQ8/DQ8). Hopefully, I have not lost you yet but if I have please continue to read on because the information that follows will still be helpful to you. What is this alpha and beta subunit typing and why is it important? HLA DQ typing consists of two subunits of the DQ molecule, an alpha and beta subunit. So, both DQ types that indicate a risk of celiac disease, DQ2 and DQ8, are made up of two protein subunits designated alpha and beta. They determine the complex letter and number combinations reported. For example, the full DQ2 molecule is typically HLA DQA1*05xx DQB1*02xx. The A1 is the alpha unit and the B1 is the beta subunit. The beta subunit is the most important component of the DQ molecule, but the alpha subunit has also been shown to carry an increased risk for celiac disease. Unfortunately, since testing for both is more complicated and expensive it is not always done. Also, some think that since the beta subunit carries most of the risk and the alpha unit only minor risk, testing for only the beta subunit is adequate. Several clinical laboratories have chosen this approach. They only test for, and report on, DQ2 and DQ8 based on beta subunit types, so their results typically look like this: HLA DQB1*02 detected, DQ2 positive, etc. This is the policy of the laboratory at Bonfils, who also does testing for Quest Diagnostics and Enterolab as well as many hospitals. However, the alpha subunit of DQ2 also carries some risk for celiac disease. What if you are positive for the beta subunit of DQ2 or DQ8 by testing from Bonfils, Enterolab or Quest? If the beta subunit is present then Bonfils, Enterolab and Quest tests will report DQ2 and/or DQ8 positive. Sometimes the report will just report DQ2 negative and DQ8 negative, especially when a hospital is reporting the results obtained from Bonfils. However, when the beta subunit is not present and they report DQ2 negative and/or DQ8 negative, it is still possible that an alpha subunit could be present. Results reported in this manner are, in my opinion, potentially misleading. I believe they can lead a doctor to assume that an individual is not at increased risk for, or cannot have celiac disease, when this may or may not be true. Unfortunately, the patient in such circumstances may be told that they can not have celiac disease, yet they may not only be at risk for the disease, they may well have it while being told it is impossible or extremely improbable. What does Prometheus do and how do they report their results? Prometheus, like Kimball and LabCorp, includes alpha and beta subunit typing. In the past they did not indicate whether there was one or two copies of DQ2 or DQ8 if someone was positive. If a patient was DQ2 and DQ8 positive then these labs reported their full genetic DQ type. However, if one or the other was negative, their exact genotype was not reported. Recently, not only has Prometheus started reporting the full DQ2 and DQ8 genotype, but they are now reporting whether someone is homozygous or heterozygous as well. They are also reporting the relative risk for celiac disease based on the pattern shown by testing. However, they are still not reporting the other DQ types. What is the advantage of the new Prometheus reporting? Since Prometheus results now include a calculation of the individual’s risk of celiac disease, compared with the general population, the patient can see how high their risk of celiac disease is, as well as being able to estimate the risk for their parents and their children. As you can see, the risk of celiac disease has a wide range of possibilities, which depend on the individual’s DQ results. This risk can be below 0.1% if you do not have any portion of the high-risk genes DQ2 and DQ8. On the other hand, the risk may be very high (more than 31 times the risk of the general population) if you have two copies of the full complement of DQ2 molecule. Again, I would like to point out that if you have DQ2/DQ2, DQ2/DQ8, or DQ8/DQ8, then both of your parents and all of your children have to have at least one copy of an at-risk celiac gene. Your child’s complete type will depend on the DQ contribution from their other parent. What other laboratories do both alpha and beta subunit testing? Kimball Genetics and LabCorp also report both alpha and beta subunit results but the advantage of their testing is that they report the other specific DQ types detected. Gluten sensitivity is found in all DQ types except DQ4. Other DQ types, particularly DQ1, DQ5, are associated with a risk of gluten related neurological and skin problems. Microscopic colitis, food allergies and oral allergy syndrome reactions are also found in association with other DQ types. Though Enterolab does report other DQ types, including these markers of risk for gluten sensitivity, they do not test for, or report, alpha subunits since their DQ testing is done by Bonfils. Based on the limited data I have accumulated so far, DQ2 and DQ8 also seem to carry a risk of mastocytic enterocolitis. What if you do not have DQ2 or DQ8? According to data accumulated, but as of February 2008, not yet published by Dr. Ken Fine, unless you are DQ4/DQ4 you are still at risk for being sensitive to or intolerant of gluten. According to Fine’s fecal gliadin antibody data all DQ types except for DQ4 carry a risk of gluten sensitivity. My clinical experience supports this claim. The presence of one copy of DQ1, DQ3, DQ5, DQ6, DQ7, or DQ9, even with one DQ4, is associated with a risk for elevated stool gliadin antibody and symptoms of gluten sensitivity that responds to a gluten free diet. What if your genetic testing was done by Enterolab, Quest, Bonfils or a hospital that utilized Bonfils, and it indicated that you were DQ2 and DQ8 negative? Since Bonfils does not test for the alpha subunit and they perform the testing for Enerolab and Quest, you may not be completely negative for DQ2 or DQ8. You do not have the beta subunits associated with the highest risk for celiac disease. For example, you could be “half-DQ2” positive and still be genetically at risk for the autoimmune form of gluten sensitivity that we know as celiac disease, along with all of its risks. What if you have not yet had celiac DQ genetic testing? I recommend that everyone have the testing. I realize that most insurance companies and doctors, including some celiac experts, would disagree with me. However, the value of DQ testing is that it can provide a great deal of information about your risk, especially if you have testing done for both alpha and beta subunits. I recommend that you have testing done by Kimball Genetics, LabCorp or Prometheus if you have not yet had genetic testing done. If your insurance or budget does not allow for this more expensive testing, but does cover testing by Quest or Bonfils or you can afford the $159 that Enterolab charges, then I still recommend that you get DQ testing using one of these laboratories. You just need to be aware of the limitations of the results as I have reviewed them here. What are the advantages of DQ testing through Kimball Genetics? Kimball can perform testing on either blood or mouth swab samples. The tests can be ordered without a doctor’s order. You can purchase testing on mouth swab sample for $345. The advantages of Kimball’s tests include alpha and beta subunit testing and full DQ typing to determine if you carry the other gluten sensitive DQ patterns besides DQ2 and DQ8. What about LabCorp? LabCorp also provides both alpha and beta subunit testing and they report the other DQ types. They only provide testing on blood samples, a doctor must order the testing, and preauthorization is required. Do health insurance companies cover celiac DQ genetic testing? Many but not all health insurance companies cover HLA DQ testing and almost all require preauthorization. The ICD9 diagnostic codes that typically are honored are V18.5 genetic predisposition for gastrointestinal disease; V84.8, genetic predisposition for other diseases; and 579.0, celiac disease. Why are the genetics so difficult to understand and why are so many doctors either unaware of the testing or reluctant to order the tests? I write and speak about DQ genetic testing frequently, and try to get testing for as many of my patients as possible. However, many insurance companies will not cover the cost of these tests. Most primary care doctors and even some GI doctors are completely unaware of the existence of a genetic test for celiac disease. The testing is difficult to understand and the reporting by some labs is very confusing and even misleading. I realize that understanding the DQ genetics is difficult for the average layperson. Most scientists and doctors don’t understand this information, so don’t despair if you are having difficulty following this or understanding your results, and don’t be surprised if your doctor does not understand them either. However, you do not need to completely understand the complexities of HLA typing to locate your DQ types on figure 1 and determine your risk of celiac disease, non-celiac gluten sensitivity, etc. Then what do you need to know or remember about celiac DQ genetics? Hopefully, you now understand enough to know that you should consider having celiac DQ testing, if possible, especially if you have symptoms, laboratory tests, or an intestinal biopsy that is suggestive of celiac disease. You should also know that the testing can be done on blood or mouth swabs, and many insurance companies will cover the testing but most require preauthorization. You should also be aware that the testing is available without a doctor’s order, if you are willing to pay for it, and that some tests are better than others. I also hope you understand that the tests can help you determine your risk for celiac disease or if you are at risk for non-celiac gluten sensitivity. You should also know that your results, especially when combined with those of one or more family members, may help you determine, to some degree, the risks for your parents and your children. You should also know what laboratories offer testing, what test codes your doctor should use to order the tests, and that the absence of DQ2 or DQ8 does not exclude risk of gluten sensitivity or intolerance. Depending on what laboratory conducts your DQ testing, your results also may fail to exclude your risk of celiac disease. What if I am still confused or I don’t know how to interpret my genetic results or my previous evaluation for celiac disease? If you are still confused by your test results or want more a personalized review of your results, symptoms or diagnostic tests I recommend that you see a physician who is an expert in celiac disease and understands these tests. I also offer on-line consultation for a reasonable fee through a secure consultation site, medem.com. You simply register (registration is free) for secure on-line communication and request a consultation. The consultation fee is $50, and some insurance companies will cover on-line communication. I also see many patients from outside of Colorado Springs for consultation if you are willing to travel here.

The following detailed explanation of serological tests for celiac disease was written by Tom Ryan, Technical Service Specialist, INOVA Diagnostics, Inc. There has been a lot of discussion about serological testing for celiac disease recently, specifically regarding tTG (tissue Transglutaminase) testing. I will try to answer some of the many questions that have appeared on this list about all of the tests. First, and this applies to any of the blood tests, you must currently be on a gluten containing diet for the tests to be accurate. Antibodies are produced by the immune system in response to substances that the body perceives as threatening. The immune response that your body produces is its response to being exposed to gluten in the diet and its subsequent effect on the intestinal mucosa. If there is no gluten in the diet, then there is no response that we can measure. A brief change in diet will not have a noticeable effect. If you have been gluten free for a week or so, it will not make any great difference. The response might be marginally less but the difference is insignificant because the body has not had time to respond to the change. Conversely, if you have been gluten free for a protracted period of time and decide to be tested, a brief challenge of a couple of weeks is not enough to elicit a response and get an accurate test. There are several steps that take place to generate an immune response and it takes time both for the positive reaction when gluten is present and to clear the antibodies when gluten is eliminated. There has been a great deal of discussion about how much and how long a challenge should be and there is no consensus. Talk with your Doctor. My personal feeling is that the minimum is 2 slices of bread per day for 6 weeks to get an accurate test but I would not try to second-guess the Doctor. There are basically four tests that can be performed to aid in diagnosing celiac disease. Notice that I say they will aid in diagnosing celiac disease. Immunology is fairly accurate but it is far from being an exact science. All of the lab tests, regardless of the type or source, are presented as aids to diagnosis. They should not be used alone as a basis for diagnosis but rather are intended to be considered in conjunction with the physical examination of the patient as well as the reported symptoms, etc. by a trained physician. There has been a great deal of confusion about what the tests are and I hope to alleviate some of the misunderstandings. There are many terms that we hear. tTG, IgA, IgG, ELISA, etc. What are all of these? Some contributors to the list make reference to the IgA or IgG test or to the ELISA test. These labels are incomplete for our purposes and could be referring to any number of different tests. We all have, within our bodies, a family of closely related although not identical proteins which are capable of acting as antibodies. These are collectively referred to as immunoglobulins. Five major types of immunoglobulins are normally present in the human adult. They are IgG, IgA, IgM, IgE and IgD. Each of these is a shorthand way of writing immunoglobulin gamma G (or A or M, etc.) and they each perform a different function in our systems. IgG is the principal immunoglobulin in human serum. It is important in providing immunity in a developing fetus because it will pass across the placental barrier. IgA is the principal immunoglobulin in secretions from respiratory and intestinal mucosa. IgE is a gamma globulin produced by cells lining the intestinal and respiratory tracts. It produces the antibodies associated with most hypersensitivity (allergic) responses. It is associated with asthma, hay fever, etc. IgM is a globulin formed in almost every immune response in the early part of the reaction. IgD is a rare protein present in normal sera in a tiny amount. These designations refer to the type of protein that is carrying the antibody in question. Both IgG and IgA subtypes of anti-gliadin antibody are produced, hence we refer to them as IgG gliadin or IgA gliadin. Collectively they are anti-gliadin antibodies. Anti-Gliadin Antibodies: Both IgA and IgG anti-gliadin antibodies (AGA) are detected in sera of patients with gluten sensitive enteropathy (celiac disease). IgG anti-gliadin antibodies are more sensitive but are less specific markers for disease compared with IgA class antibodies. IgA anti-gliadin antibodies are less sensitive but are more specific. In clinical trials, the IgA antibodies have a specificity of 97% but the sensitivity is only 71%. That means that, if a patient is IgA positive, there is a 97% probability that they have celiac disease. Conversely, if the patient is IgA negative, there is only a 71% probability that the patient is truly negative for celiac disease. Therefore, a positive result is a strong indication that the patient has the disease but a negative result does not necessarily mean that they don not have it. False positive results are rather uncommon but false negative results can occur. On the other hand, the IgG anti-gliadin antibodies are 91% specific and have an 87% sensitivity. This means that they will show positive results more readily but there is not as strong a correlation with celiac disease. It is less specific. Patients with other conditions but not afflicted with celiac disease will occasionally show positive results. IgG anti-gliadin antibodies are detectable in approximately 21% of patients with other gastrointestinal disorders. This test might yield false positive results but is less likely to yield false negative results. A sensitive testing protocol includes testing for both IgA and IgG anti-gliadin antibodies since a significant portion of celiac patients (approx. 2-5%) are IgA deficient. This combined IgA and IgG anti-gliadin antibody assay has an overall sensitivity of 95% with a specificity of 90%. The type of test used to detect the anti-gliadin antibodies is called an ELISA. This is an acronym and it stands for Enzyme Linked Immuno-Sorbent Assay. ELISA is not a test in itself. It is a method of testing and it is a relatively simple test to perform. It involves putting a measured amount of diluted patient serum into the wells of a specially constructed and prepared plate and incubating it for a period of time with various chemicals. The end result is a color change, the intensity of which is dependent upon the concentration of anti-gliadin antibody (or other protein being measured) in the patient serum. The ability of this colored solution to absorb light at a particular wavelength can be measured on a laboratory instrument and mathematically compared with solutions that contain a known amount of anti-gliadin antibody to arrive at a number for the amount of antibody present. The sample can then be classified as negative, (0-20 units); weak positive, (21-30 units); or moderate to strong positive if greater than 30 units. The purpose of testing for anti-gliadin antibodies includes, in addition to diagnosis of gluten sensitive enteropathy, monitoring for compliance to a gluten free diet. IgA gliadin antibodies increase rapidly in response to gluten in the diet and decrease rapidly when gluten is absent from the diet. The IgA anti-gliadin antibodies can totally disappear in 2-6 months on a gluten free diet, so they are useful as a diet control. By contrast, IgG anti-gliadin antibodies need a long time, sometimes more than a year, to become negative. The reverse is also true. That is, a patient with celiac disease who has been on a gluten free diet and tests negative for IgA anti-gliadin antibodies, will show a rapid increase in antibody production when challenged by gluten in the diet. Approximately 90% of challenged patients will yield a positive IgA anti-gliadin result within 14-35 days after being challenged. The IgG antibodies are somewhat slower. Endomysial Antibodies: IgA class anti-endomysial antibodies (AEA) are very specific, occurring only in celiac disease and DH. These antibodies are found in approximately 80% of patients with DH and in essentially 100% of patients with active celiac disease. IgA endomysial antibodies are more sensitive and specific than gliadin antibodies for diagnosis of celiac disease. Antibody titers (dilutions) are found to parallel morphological changes in the jejunum and can also be used to reflect compliance with gluten-free diets. Titers decrease or become negative in patients on gluten free diets and reappear upon gluten challenge. The test for anti-endomysial antibodies is more subjective and more complicated for the lab to perform than the anti-gliadin assays. It involves serially diluting some of the patients serum, that is, diluting it by ½ then ¼, 1/8, 1/16, etc. and putting these dilutions on a glass slide that has some sort of tissue affixed to it. The slide is then processed with various solutions and examined under a fluorescent microscope to determine if any of that serum binds to any of the proteins in the tissue. If so, then that patient is confirmed as having antibodies to that particular protein. This method of testing is called an IFA or sometimes IIFA. It stands for Indirect Immuno-Fluorescent Assay. The selection of which tissue slide to use is determined by what specific protein, hence which antibody, you are specifically looking for. Endomysial antibodies react with the endomysium, which is a sheath of reticular fibrils that surround each muscle fiber. Therefore, to detect endomysial antibodies, you would want to use a tissue substrate that contains a lot of muscle tissue. The substrate used most often for this assay is distal sections of the esophagus. These are very thinly sliced and fixed to the slide. They contain muscle fibers and not much else so there is a lot of endomysium available to react with the anti-endomysial antibodies. Reading this test involves viewing the reacted slides with a fluorescent microscope to make the determination. This requires a highly skilled and trained eye and, of necessity, is somewhat subjective. You are looking for a green fluorescence in the endomysium covering the muscle fibers. The test is reported as the titer or final dilution in which the fluorescence can still clearly be seen. As you can imagine, this is very subjective. There are no standardized values and it is up to the judgment of the particular technician what the endpoint titer is. Recently, (1998) the endomysial antigen targeted by the anti-endomysial antibodies was identified as the protein cross-linking enzyme known as tissue transglutaminase (tTG). This has enabled the production of an antigen specific ELISA assay incorporating tTG as a reliable and objective alternative to the traditional and subjective Immunofluorescence based assays. In clinical trials, the correlation with the endomysial IFA assay has been shown to be close to 100%. This is a test that has been very well received in the professional community. It is an ELISA, like the anti-gliadin antibody test and, as such, is not subject to interpretation like the IFA. That is the greatest advantage to this new test! With this or any ELISA, the response is measured on an instrument that calculates the amount of light of a particular wavelength that is absorbed by the solution and prints out a numerical result. There is no chance of human error skewing the results because there is no judgment call involved. The ELISA plate, regardless of what you are testing for, is processed with at least three control sera (sometimes as many as eight) in addition to the unknown sample being tested. There is a negative serum and at least two positive sera containing different levels of the antibody being tested. There are specific requirements for the absorption levels of these three controls. That is, each of them has a minimum or maximum (or both) number that must be seen by the instrument in order for it to be a valid test. If there is any variance from these expected numbers, it is an indication that something went wrong and the test results are discarded and the test repeated. There is therefore no way the technician could report inaccurate results, (assuming they diluted the sample correctly). Either the test was valid, and you can rely upon the accuracy of the result, or the test is invalid, and the entire result discarded. If any error was made during the processing of the ELISA plate, it would result in the control sera numbers being out of range and the entire test result would be thrown out. In summary, the tTG ELISA is measuring the same thing that the endomysial IFA is measuring but with a method that is more sensitive and specific and not subject to interpretation. IgA class Reticulin antibodies are found only in Celiac disease and dermatitis herpetiformis. These antibodies are found in approximately 60% of celiac disease patients and 25% of DH patients. This test is falling into disuse because of the limited utility and the availability of better tests. It is an IFA performed on a tissue substrate with all the attendant problems that go along with it. The development of all of these serum assays has tremendously simplified the diagnosis of celiac disease and improved the accuracy as well. The original criteria for diagnosis according to the European Society for Pediatric Gastroenterology and Nutrition, (ESPGAN), involved a year of arduous studies with: An initial positive gut biopsy; 6 months on a gluten free diet; A second, negative gut biopsy; A gluten challenge for 6 months and; A third, positive gut biopsy. The revised ESPGAN criteria call for positive results in two of the serological tests confirmed by a single positive biopsy. In practice, many gastroenterologists are utilizing the serologies in conjunction with a controlled diet and the clinical presentation to form a basis for diagnosis without the need for the invasive procedure. Through the auspices of the Celiac Disease Foundation and others, a professional symposium and workshop was organized earlier this year in Marina Del Rey, California with participants from Europe as well as the U.S. to establish standards for reporting test results. This should improve testing and diagnosis even more. At the conclusion of this conference a Celiac Disease Standardization Committee was formed to investigate and make recommendations on a standardized method of reporting results.