IgG Food Allergy Testing by ELISA/EIA
نویسنده
چکیده
Adverse reactions to food may initiate a myriad of physiological effects in the body. These reactions may be immunologically or nonimmunologically mediated and can result in signs and symptoms ranging in severity from mild to life threatening anaphylaxis. Although the majority of severe reactions are thought to be immunological and mediated via IgG and IgA may play a role in adverse reactions to food as well. The clinical laboratory has historically played an important role in the diagnosis and management of patients with allergy. This role has been more clearly defined with the diagnosis of IgE mediated adverse reactions and less well defined with the diagnosis of other immunologic etiologies or adverse reactions of non-immunologic origin. Diagnosis of food allergy, in particular, has classically involved the detection of IgE antibodies with a variety of different methodologies. Of late, a number of clinical laboratories have set up ELISA/EIA (Enzyme Immunoassays) panels to test the presence of IgG antibodies in patients to numerous food allergens. This is based on the findings that certain subclasses of IgG have been associated with the in vitro degranulation of basophils and mast cells, the activation of the complement cascade, (both of which are important mechanisms in allergy and anaphylaxis and the observation that high circulating serum concentrations of some IgG subtypes have been measured in certain atopic individuals. The premise behind this testing is that high circulating levels of IgG antibodies are correlated with clinical food allergy signs and symptoms. These tests, one might extrapolate, would help the physician pinpoint food allergies in their patients so that patients might avoid these foods and their associated signs and symptoms. The ELISA/EIA test itself involves coating a 96 well plate with food antigens, adding a patient’s sera and looking for a classic antigen/ antibody interaction. In addition to the IgG antibody detected in most of the newer commercial assays, some companies also detect IgE. Food allergy panels have found an increasing popularity among physicians who are looking for a reliable method to aid in the diagnosis of an otherwise difficult diagnostic problem. Up until now, the only methods for the detection of food allergy included skin tests, elimination and challenge diets, or double blind placebo controlled oral food challenges. Skin tests, although fairly reliable for the detection of IgE to environmental allergens, are not well correlated with food allergy signs and symptoms. Placebo controlled food challenges and elimination/ challenge diets are extremely time consuming for the patient and practitioner and elimination/ challenge diets require a high degree of patient motivation and compliance. The detection of food allergies with the use of food allergy panels, in contrast to the previously mentioned methodologies, is easy and convenient for both patient and physician. One need only submit a blood sample from the patient and the laboratory returns not only the foods the patient is “allergic to” but a “rotation” or “elimination” diet for the patient. The cost is moderate to high, running on average between $100 and $400 per panel. The use of these food allergy panels for the diagnosis and management of food allergies, however, is fraught with problems. These problems include reliability in testing, an arguable theory behind the testing and the prevalence of treatments (food rotations or other diets) prescribed by these testing laboratories based solely on laboratory test results. This article will address these problems and others.
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