Food Allergy Testing
Many physicians order blood tests looking for antibodies indicating sensitization to certain foods, and when such antibodies are found the physicians inform the patients to avoid those foods. Blood tests alone, however, are not diagnostic for food allergy, Sampson said, and many people with sensitivities to certain foods will not actually have a reaction upon exposure.
“The exercise of diagnosing a food allergy is not just doing a skin test, or not just doing a blood test, or not even just having a report of a food allergy,” Sampson said. “It takes a combination of a good medical history as well as some laboratory tests and in some cases an oral food challenge in order to make the appropriate diagnosis.”
In fact, the guidelines called for the use of medical history and physical examination to aid in the diagnosis of food allergy and to confirm patient-reported food allergy.
The recommendations also addressed the use of multiple types of tests for reaching a diagnosis for IgE-mediated food allergy:
• A skin prick test should be used to identify foods that may be provoking an allergic reaction, but it cannot stand alone for diagnosis. Intradermal testing and routine use of measuring total serum IgE should not be used to make a diagnosis.
• Allergen-specific IgE tests should be used to identify foods that could potentially provoke allergic reactions, but are not diagnostic of food allergy alone.
• An atopy patch test should not be used in routine evaluation of noncontact food allergy.
• A combination of skin prick tests, allergen-specific IgE tests, and atopy patch tests should not be used for routine diagnosis.
• Several nonstandardized and unproven procedures should not be used for diagnosis, including the allergen-specific IgG4 test used by some clinicians.
• Oral food challenges should be used for diagnosing food allergy. A double-blind, placebo-controlled food challenge is the gold standard, although a single-blind or open food challenge may be considered diagnostic in two cases: if either of these challenges elicits no symptoms, then food allergy can be ruled out. But when either type of food challenge elicits symptoms consistent with medical history and are supported by lab tests, then a diagnosis of food allergy is supported.
During the conference call, Sampson said he believed that many physicians avoid performing oral food challenges because they are time consuming, place the patient at some risk, and are not well compensated.
In terms of treatment, the guidelines noted that no drugs have been shown to prevent a reaction in patients with a food allergy. Allergen avoidance is the first-line treatment, and antihistamines are used for managing nonsevere food-induced allergic reactions.
Although recent studies of immunotherapy have yielded promising results, the guidelines stated that the evidence is not strong enough to recommend using allergen-specific immunotherapy to treat IgE-mediated food allergy.