FCAAIA Notes: The best test for diagnosis of food allergy is a thorough history as to what happens with ingestion. Tests for food allergy can help confirm or refute a diagnostic suspicion (which means the physician needs to have a diagnostic suspicion before doing the test). The results are not “black and white” but require interpretation in the context of the patient’s history. A positive does not mean you have allergy. If you do not have symptoms with ingestion you are not allergic. Sometimes, we have enough information from skin and/or blood tests to be highly suspicious of food allergy and are therefore hesitant to do a food challenge.
However, you do not necessarily need to avoid all food to which you have a positive test. In fact, if you eat a food and nothing happens, you almost never need to be tested to that food.
Are you avoiding a food only because of a positive test? Should you be retested and/or have a food challenge? The answers will depend on the individual, but talk to your allergist about whether you are avoiding too many foods merely because you had positive tests.
(Source: http://www.medscape.com/viewarticle/883310?nlid=117067_3821&src=WNL_mdplsfeat_170801_mscpedit_aimm&uac=112079PK&spon=38&impID=1401582&faf=1 August 1, 2017. For Medscape articles: User name: FCAAIA, Password: Allergies)
A consensus report on critical issues in food allergy was released by the National Academies of Sciences, Engineering, and Medicine. A summary of that report was published online July 24 in Pediatrics.
Scott H. Sicherer, MD, professor of pediatrics, allergy, and immunology, Icahn School of Medicine at Mount Sinai in New York City, and colleagues participated in the development of the consensus report, which was targeted to many different stakeholders in food allergy, including industry, government, and patients. The authors felt it was important to bring forth relevant highlights for physicians managing pediatric patients with possible food allergies.
“What we tried to do in this article is focus on a few of the critical things that pediatricians might be interested in and be thinking about,” Dr. Sicherer told Medscape Medical News.
“And it’s very important for physicians to take a judicious history in the context of knowledge about food allergy and then judiciously select tests that make sense to confirm suspected allergies, rather than test with panels without any thought about the history and epidemiology of food allergy,” he added.
One of the most relevant highlights of the report is the issue of diagnosis, the authors write.
“A serious misconception about food allergy diagnostics relates to equating a ‘positive test result’ by a serum food-specific [immunoglobulin E] (sIgE) blood test or skin prick test…to having an allergy to the tested food,” they explain. “These tests detect IgE antibodies to the food but are not typically intrinsically diagnostic,” they add.
The authors cite a study in which 111 oral food challenges were performed in 44 children who were avoiding a specific food because they had tested positive on either an sIgE blood test or a skin prick test.
Results showed that 93% of this small group could tolerate the food they had been avoiding because of the “positive” allergen test. “It is clear that these tests are misunderstood by physicians,” the current report authors write. However, physicians also risk underdiagnosing or misdiagnosing a true food allergy. Without confirmatory testing, an allergen could incorrectly be identified as the culprit, leading to a serious reaction if the child is again exposed to the true allergen.
“Medical history is key in diagnosis, and food allergy should be considered when allergic symptoms occur proximate (within minutes to hours) to ingestion of a specific food, especially when symptoms occur on more than 1 occasion,” the authors write. Physicians involved in pediatric care also need to remember that not all food allergies evolve from the production of IgE antibodies, and these will be missed on IgE antibody-based tests. Examples of non-IgE-mediated allergies include protein-induced enterocolitis, symptoms of which start 2 hours after ingesting the offending food allergen, and allergic colitis, characterized by mucous-containing bloody stools.
In contrast, “food allergy is not a typical trigger of chronic asthma or chronic rhinitis in childhood,” the researchers note.
The oral food challenge or feeding test is the definitive test to confirm an infant or child really does have a food allergy, Dr. Sicherer said. “But in the vast majority of cases, a food allergy can be excluded or diagnosed with pretty good accuracy when you put together a careful history and [either sIgE or skin prick] testing,” he said. A feeding test is really only needed when the patient’s history or test results or both are ambiguous.
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