What is the Process of Food Allergy Testing?
An accurate diagnosis history of food allergy begins with a detailed history of specific symptoms associated with consuming specific foods. A food allergy evaluation should be performed by a board certified allergist with expertise in evaluating and managing food allergies. A diagnosis of food allergy is not made by simply ordering a panel of blood tests, as the results of these tests must be correlated with the patient’s history of allergic reactions to the food(s) in question. In the absence of a correlating, the predictive value of a positive food allergy test is not much better than 50%. A positive allergy test for a food suggests the possibility of an allergic reaction, but does not predict the severity of that reaction nor the amount of food required to trigger it.
Symptoms of a food allergic reaction typically start within a few minutes after eating the allergenic food. Such reactions usually include itching and/or swelling of the mouth, throat and face and may progress to wheezing, difficulty breathing, abdominal cramping, nausea, vomiting and even anaphylactic shock. Severe allergic reactions may be triggered by ingesting tiny amounts of food protein. The most common foods causing more than 85% of allergic reactions include milk, egg, wheat soy, peanut, tree nuts, fish and shellfish.
The most up-to-date best practices in the diagnosis and management of food allergies can be found in the 2014 Food Allergy Practice Parameters published jointly by the two largest professional societies of board certified allergy/immunology specialists. Here’s a helpful list of what to expect as you begin an evaluation for suspected food allergy.
Describe your symptoms. Be prepared to tell your doctor a history of your symptoms — which foods, and how much, seem to cause problems — and whether you have a family history of food allergies or other allergies.
Physical examination. A careful exam can often identify or exclude other medical problems.
Food diary. Your doctor may ask you to keep a food diary of your eating habits, symptoms and medications to pinpoint the problem.
Food allergy skin testing. A skin prick test can help determine your risk of an allergic reaction to a particular food. In this test, a small amount of an extract of the suspected food is placed on the skin of your forearm or back. Your skin is then pricked with a needle to allow a tiny amount of the substance beneath your skin surface. A positive skin test response to a food suggests a potential risk of an allergic reaction but does not by itself constitute a diagnosis of food allergy.
Serum IgE food allergy testing. As an alternative to allergy skin testing, a blood test can measure levels of allergic antibodies (known as IgE) for specific foods in question. For this test, a blood sample is sent to a medical laboratory. Serum IgE antibodies to foods are a bit less sensitive than skin testing in detecting allergic sensitivities. However, these tests are ideal for predicting the likelihood of losing allergic sensitivity over time. Serum IgE allergy testing is also preferred for patients who are taking certain medications that interfere with allergy skin testing and cannot be discontinued.
Elimination diet. You may be asked to eliminate suspect foods for a week or two and then add the food items back into your diet one at a time. This process can help link symptoms to specific foods. However, this isn’t a foolproof method. Psychological factors as well as physical factors can come into play. For example, if you think you’re sensitive to a food, a response could be triggered that may not be a true allergic one. If you’ve had a severe reaction to a food in the past, this method may not be safe.
When the patient’s allergy testing results do not appear to support a diagnosis of food allergy or if there is a question as to whether or not a food allergy has resolved, a graded oral food challenge (OFC) procedure can definitively settle the question. Oral food challenges should only be performed under the supervision of board certified allergists who are experienced in conducting these tests and treating anaphylactic reactions. During the OFC you’ll be given small but increasing amounts of the suspect food followed by 1 to 2 hours of observation in the office If you do not experience an allergic reaction you may be able to include this food in your diet again.
Food allergy testing is an important step if you or someone you know suspect food allergies. Rely on the experts who specialize in food and other allergies to recommend your best course of treatment.