Testing for wheat allergy and celiac disease
So you or your doctor thinks you might have a problem with wheat or gluten. How can you tell?
Wheat Allergy
Blood tests for all allergies show the amount of IgE antibody that is circulating in the blood stream. It is this type of antibody that reacts when you eat wheat or an allergic food. Another type of blood tests is for IgG reactions to foods. This test is less reliable than the IgE to confirm an allergy.
Skin prick tests can confirm IgE allergies, as long as the patient is not on an antihistamine or similar medicine. Occasionally, allergists will also do patch testing. This is where they put a small amount of the fresh food on the skin to check for a reaction. And sometimes, allergists will try a food challenge in their office where they will give the food in small, increasing quantities to see if there is a reaction.
Gluten Intolerance/Celiac Disease
Blood tests for celiac disease have gotten progressively more accurate. We have fewer tests and get better results.
Tissue Transglutaminase (tTG), the enzyme that acts on gluten, forms an antibody that is 97% accurate in suggesting who might have celiac disease. Two forms exist, the IgA and IgG, and if either is significantly elevated, an intestinal biopsy is usually done to confirm the diagnosis. Since this is in part a genetic condition, some doctors will diagnose 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, 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.
<<Non-celiac gluten sensitivity>> requires a strict elimination diet for 3-4 weeks after excluding these other conditions.
Stool tests for gluten are not routinely accepted as evidence of celiac disease because they have not been proven to be accurate. 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
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.
Other tests
Your doctor may also want to run other tests. 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 and nutrient losses. Since uncontrolled or unrecognized celiac disease can affect how your liver functions, your doctor may want to check your liver with blood tests as well.
