Identifying Food Allergens

For determining the food antigens to which a patient is susceptible, food-allergy tests are performed to determine a patient's allergies sensitively and specifically. Modern serum testing, used with detailed history taking and analysis of a patient's symptomatology, can expedite a diagnosis of food allergy. This approach is helpful because symptoms of such allergies are typically quite difficult to isolate and explain via food-ingestion-related causes and effects, because of the delayed reactions that are typically involved. Laboratory and challenge tests can provide reliable information to help identify both suspected and unsuspected food allergens. Although standard laboratory tests, such as the RAST and ELISA are simple for a patient, tests that entail challenging a patient with antigenic foods, either orally or dermally, are much more difficult or may not provide adequate specificity to identify offending food allergens. For example, the two common offenders, wheat and soy, are so prevalent in foods (under different names), that in recalcitrant cases, it is necessary to utilize laboratory tests to identify additional reactive foods. This is especially true because some patients have allergies to food other than the most common culprits that might not be removed in elimination diets. A study was carried out to compare the efficacy of the ELISA versus the skin-prick test to cow's milkproteins in 41 children with suspected allergy. The patients were simultaneously evaluated by skin-prick testing with scratch test antigen to whole CMP. Although only 13 (32%) of the 41 patients were positive by the skin-prick test, 25 (61%) were positive by the IgE ELISA. Of the 25 IgE ELISA-positive patients, 20 were also positive by the IgG ELISA. There was concordance of positive results between skin testing and the IgE ELISA in 9 patients (22%), and there was concordance of negative results in 12 patients (29%). Discordant results were found in 20 patients (49%). These results indicate that the ELISA is more sensitive than skin-prick testing in the identification of individuals with elevated levels of IgE to CMP.34 An additional study examined RASTs testing with elimination diets based on the results of the test in 114 patients. The results demonstrated a 71% success rate for all symptoms achieving at least a 75% improvement of symptoms. In the group of patients with chronic, disabling symptoms that were unresponsive to other intensive treatments, 70% obtained 75% or more improvement of symptoms and 20% of these patients obtained 100% relief.35 See the box on pages 200-201 entitled "Allergy Detection Tests'' for more information about the different tests that are available, how they are performed, and their utility.

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