It is becoming increasingly common to find products in grocery stores that advertise themselves to be free of allergens such as gluten, dairy, eggs, or nuts. At least 20% of Americans alter their diets in response to perceived food intolerances. Although many symptoms of food allergies are well known, food allergies can also contribute to complex conditions such as chronic fatigue syndrome and headaches. Three common testing techniques–skin prick testing, blood testing, and food challenges—can help you find out if food allergies are at the root of your symptoms.
What is a food allergy?
A true food allergy, also called a food hypersensitivity reaction, is due to an adverse immune response. The immune system has Y-shaped proteins called antibodies that identify foreign matter in the body. When these antibodies mistakenly flag proteins found in ingested food as dangerous, the body mounts an immune response against the food.
In an immediate hypersensitivity reaction, IgE antibodies activate mast cells in areas like the skin, respiratory tract, and cardiovascular system. This type of potentially life-threatening response can lead to a rapid onset of swelling, itching, and difficulty breathing. Food allergies can also lead to delayed immune reactions, which are mediated by different antibodies, such as IgG. The symptoms from this type of allergy can take as long as many days to appear.  Delayed reactions may present as digestive problems, headache, fatigue, or a variety of other symptoms. Most allergy tests work by testing for the presence of antibodies specific to certain foods.
Skin prick test
Skin prick tests have been widely used for food allergies that are mediated by IgE antibodies. This test involves pricking the skin and exposing the body to the allergen in question. If IgE antibodies are activated in the area of the prick, the skin develops a mark called a wheal. This is considered a positive result.
The advantages of skin testing are that it is minimally invasive and results can be available within minutes. However, a negative result from a skin prick test does not necessarily mean that the individual is not allergic to that food. Skin prick tests are most useful when combined with patient history and physical examination, and as a confirmation of a suspected food allergy.
Blood serum tests
Serum testing is a newer technique that research shows to be more sensitive than skin prick testing. For food allergy testing, blood is drawn and sent to a laboratory for ELISA testing. This test measures the levels of either IgE or IgG antibodies for specific foods. The amount of circulating IgE or IgG antibodies specific to a food serves as an indication of whether or not the individual is mounting an immune response against that food. Again, physical examination and clinical history of the patient are important in interpreting and verifying results.
The double-blind, placebo-controlled, oral food challenge was previously considered the gold standard for diagnosing food allergies. It is no longer the first choice test, due to risk of dangerous reactions and difficulty standardizing the testing. However, the food challenge may be especially helpful if other tests have failed to provide conclusive results. In the food challenge, the patient is given doses of food allergens or placebo at 20-minute intervals while they are observed for signs of reaction. If the patient tolerates all of the doses of the allergen, they then eat a regular-sized portion of the food to confirm tolerance. The food challenge can only test for immediate reactions, not delayed reactions.
If you have unexplained symptoms or suspect that certain foods are negatively affecting your health, ask your doctor about food allergy testing. You can also use our directory to find integrative physicians and practitioners who are knowledgeable about food allergies and can help you find the answers you need.
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