So you or your doctor (or your neighbor's second cousin) thinks you might have a problem with wheat or gluten. How can you tell?
You may be familiar with tests for wheat allergy. Blood tests for allergies all show the amount of IgE antibody that is circulating in the blood stream. That's IgE antibody, because those are the factors that seem to be what reacts in an allergic event, where you have a actual reaction to eating wheat. There's also blood tests for IgG reactions to foods, but most allergists feel these are not worthwhile and show only that you've recently had that food rather than any reaction to it. Other practitioners may agree that it's not a true allergy but that the test may suggest you are more likely to have a sensitivity to that food.
Skin prick tests usually pick up similar IgE allergies, as long as the patient is not on an antihistamine or similar medicine at the time. Occasionally, allergists who deal with a lot of food reactions will also do patch testing where they will put a small amount of the fresh food on the back to test if the person will have a reaction that can go along with a condition known as eosinophilic esophagitis (covered in a separate post).
And sometimes, allergists will try a food challenge in their office or another safe place, where they will give you the food in increasing (but small quantities) to see if they can provoke some of the symptoms you describe with that food.
The blood tests for celiac disease have gotten progressively more accurate. We have been able to hone in on fewer tests and get better results.
Tissue Transglutaminase (tTG), which is the enzyme that acts on gluten, forms an antibody that is 97% accurate in suggesting which individuals might have celiac disease. Two forms exist, the IgA and IgG, and if either is significantly elevated, one should be suspicious that the person has celiac disease, with an intestinal biopsy performed to confirm the diagnosis in most instances. Since this is in part a genetic condition, some doctors will make the diagnosis on a family member without a biopsy, if they have an elevated tTG level and someone else in the family already has had a biopsy.
Two notes of caution
- This test is not very helpful for the initial diagnosis in someone who has already restricted gluten from their diet.
- The IgA fraction will be low in someone who has an immune defect involving their IgA (and they will be 10 times more likely to have celiac disease.
The Endomysial Antibody, which is antibody to gastrointestinal tissue, may be positive in someone who is already on a gluten-free diet. Thus, it is helpful if it is positive, but is meaningless if it is negative .
The antigladin antibody level is an interesting test since it reflects a reaction to the fraction of wheat gluten that actually causes the intestinal damage. In young children, we will occasionally find an elevated IgA antibody to gliadin before the tTG shows up. The problem is that often we are confronted with increased IgG antibodies to gliadin. When they are strikingly elevated, that can be indicator of celiac or non-celiac sensitivity, but at lower levels they can be normal or can show that some other allergy or problem is causing a reaction in the small intestine.
Non-celiac gluten sensitivity requires a strict elimination diet for 3-4 weeks after excluding these other conditions (as discussed in another blog post).
Stool tests for gluten are not routinely accepted as evidence of celiac disease because they have not been proven to be sensitive or specific enough. In the same way that the IgG test for antigliadin antibody can be positive in normal people, and lead them to think they have celiac disease, the stool tests can potentially do the same--and they might miss those who actually have gluten sensitivity.
Genetic testing for celiac disease is available, but the problem is that 1/3 of everyone has the gene that allows them to develop celiac disease. So the test should not be routinely performed--but it is useful in 2 settings. Someone in the family has been diagnosed and the doctor is trying to find who else in the family might have it. This is particularly important if a child is diagnosed, since one of the parents by definition, should have the gene. Second, a negative test strongly suggests that the person is in the other 2/3 who will never get celiac disease, and that is useful to know in someone who might have bad intestinal problems and negative tests for celiac disease, so that the doctor knows that the tests for celiac disease don't have to be repeated in the future.
Your doctor may also want to run other tests if you have celiac disease or if he/she is concerned you might. He might test your iron levels because iron is absorbed in the intestinal area where celiac disease does the most damage. Other nutrients (vitamin D, B12, Folate, Zinc) may be tested to assure you are absorbing them. Similarly, your stool may be tested to make sure you are not having a problem absorbing fat (that provides evidence that you are at risk for multiple nutrient losses). Since uncontrolled or unrecognized celiac disease can affect how your liver functions and because autoimmune liver disease can occur with celiac disease, your doctor may want to check your liver with blood tests as well.
Bottom line: Reliable tests for celiac disease and its consequences are available. At the same time, some commercial tests are marketed, but they are not sensitive or specific enough.