Wednesday, January 5, 2011

Food Allergy: The Definitive Guide to Clinical Practice

From Medscape Allergy & Clinical Immunology

Laura A. Stokowski, RN, MS

* The Definitive Guide to Clinical Practice in Food Allergy
* A Uniform Definition of Food Allergy
* A Reliable Approach to Diagnosis
* A Consistent Management Plan
* Misconceptions and Misunderstandings About Food Allergy
* Emergency Management of Severe Reactions and Anaphylaxis
* What Do the Guidelines Mean to Practitioners and Patients?
* References

The Definitive Guide to Clinical Practice in Food Allergy

As many as 90% of self-reported food allergies might not be allergies at all. So -- if they aren't food allergies, what are they, and why does this level of misunderstanding exist?

True food allergies affect only about 5% of children and 4% of adults in the United States.[1] Some experts speculate that the incidence might be increasing, but want of a uniform definition for food allergy has hampered the determination of its actual rates.

That is, until now. The National Institute for Allergy and Infectious Diseases (NIAID) has just released its Guidelines for the Diagnosis and Management of Food Allergy in the United States ,[2] the much-anticipated culmination of a 2-year effort on the part of medical organizations, federal agencies, and patient advocacy groups.[3]

The real value of the guidelines is that they are written not just for allergy specialists, but also for general and specialty practitioners in other fields -- such as primary care, dermatology, gastroenterology or emergency medicine -- who often encounter patients with symptoms or claims of food allergy or food reaction. The guidelines define food allergy and distinguish it from other adverse food reactions, spell out the diagnostic process for potential food allergy (which tests are useful and which are not), and describe the "best practices" for management of food allergy and its symptoms, including anaphylaxis.

"Previous food allergy guidelines were developed by allergists for allergists," explained Matthew Fenton, PhD, Chief of the Asthma, Allergy, and Inflammation Branch of the Division of Allergy, Immunology, and Transplantation, NIAID, and one of the guideline's authors. "This is a major advance, and one that I hope will translate into better patient health and patient care. This effort represents the biggest and broadest attempt to develop evidence-based guidelines -- guidelines that are based on data that has been thoroughly reviewed and graded by experts and that also incorporates expert clinical opinion. Most importantly, this process was conducted by healthcare professionals across a wide range of specialty areas -- everyone who is involved in food allergy, from the advocacy groups to the government public policymakers to the clinical practitioners. It is a departure from previous guidelines. We want the family practice physician in Fargo, North Dakota, to pick up the guidelines and use them as easily as the allergy specialist in Manhattan."

"The guidelines put as much emphasis as possible on evidence-based information, complemented by expert opinions," added American Academy of Allergy and Clinical Immunology President Sami Bahna, MD."They will be very useful to allergists as well as other practitioners because the guidelines incorporate updated literature that has been critically interpreted."

Food allergy doesn't have a cure, or even, in a conventional sense, a treatment. It boils down to proper diagnosis, on the basis of a uniform definition, and management that is consistent and safe for the patient, and most of all, backed up by scientific evidence.
What Do the Guidelines Offer?

The guidelines offer exactly what most practitioners need -- criteria for food allergy that clear up questions such as what is a true food allergy, and what isn't a food allergy at all? They provide reliable diagnostic strategies for patients with reported food allergies -- which tests are useful, which are not -- and when it is best to refer to a specialist. The guidelines outline a consistent approach to management of food allergy, including the appropriate and timely response to severe food allergy symptoms and anaphylaxis. Finally, the guidelines clear up common misconceptions about food allergy, and answer lingering questions such as "is it possible to prevent food allergy"?

A Uniform Definition of Food Allergy

When the scientific literature was examined to identify best practices related to food allergy, many divergent definitions for "food allergy" were found. The first task, therefore, was to define food allergy:

An "adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food." [2]

A food is any substance that is intended for human consumption, and may include drinks, chewing gum, food additives, and dietary supplements. A food allergen is the specific component of or ingredient in food (protein or chemical hapten) that is recognized by allergen-specific immune cells and elicits specific immunologic reactions (mediated by immunoglobulin E [IgE] antibodies and/or T cells), resulting in characteristic symptoms.[2]

A food allergy reaction occurs minutes to hours after smelling, touching, or ingesting a specific food -- the trigger -- and results in symptoms of hives, itching, trouble breathing, wheezing, or even anaphylaxis. A food allergy reaction is reproducible; the trigger does not change, and the trigger always sets off the same immune response. Even so, the intensity of a response can vary from event to event.

The guidelines point out that "because individuals can develop immunologic sensitization (as evidenced by the presence of allergen-specific IgE (sIgE) to food allergens) without having clinical symptoms on exposure to those foods, an sIgE-mediated food allergy requires boththe presence of sensitization andthe development of specific signs and symptoms on exposure to that food. Sensitization alone is not sufficient to define food allergy."[2]

Also provided are concise definitions for food allergy syndromes, including food-induced anaphylaxis, gastrointestinal food allergies (immediate gastrointestinal hypersensitivity, eosinophilic esophagitis, eosinophilic gastroenteritis, dietary protein-induced proctitis, food protein-induced enterocolitis syndrome, oral allergy syndrome), cutaneous reactions to food (acute urticaria, angioedema), and respiratory manifestations of food allergy.
Food Allergy vs Food Intolerance

The 50% to 90% of self-reported food allergies that are not really allergies are actually reactions to food that are not mediated by the immune system. This is the critical difference. Non-allergic food reactions, referred to as "food intolerances," typically occur 3-4 hours after ingesting a certain food or similar food and produce symptoms that vary depending on the nature of the intolerance. "With the exception of lactose intolerance, not much is known about other food intolerances," admitted Dr. Fenton. "These people aren't overreacting; it's a real disease. Food intolerances are quite common and can share symptoms with food allergy."

Because they can mimic immune reactions, food intolerances are often confused with food allergies, but the underlying mechanisms differ. Food intolerance can be metabolic, pharmacologic, or toxic in nature, and can involve components of food or additives such as lactose, caffeine, monosodium glutamate, tyramine, artificial colors, or sulfites.
A Reliable Approach to Diagnosis

"With all the attention to food allergy in the press, more people are asking to be tested," observed Dr. Fenton. "It can create stress; people are afraid to eat certain foods."
History and Physical Examination

A detailed medical history and physical examination are the starting points in a patient with possible food allergy, although the findings of neither can be considered diagnostic of food allergy. Parent or patient reportsof self-diagnosed food allergies have low positive predictive value and must be confirmed by other means.[2] A table of systems-specific food allergy symptoms can be found in the guidelines. An individual presenting with any combination of these symptoms shortly after ingesting a food should be evaluated for food allergy, particularly if the symptoms have occurred on more than a single occasion. The guidelines emphasize that diagnosing food allergy on the basis of history or physical examination alone can lead to erroneous diagnosis of food allergy and result in unnecessary dietary restriction that could have adverse nutritional consequences.[2]
Objective Testing

A practical feature of the guidelines that will be invaluable to clinicians is information about which "food allergy tests" have been scientifically validated to make a diagnosis of food allergy and which have not.

"We often hear from practitioners who ask about various products and tests on the market that purport to diagnose food allergies," explains Matthew Fenton. "It is astounding how many products that claim to be diagnostic or therapeutic are not supported by the evidence. So the new guidelines narrow the list to those things any physician would want to use to diagnose and manage food allergy. Practitioners are relieved to hear this, because they are bombarded with these useless products."

Confusion persists about some commonly employed food allergy tests. Dr. Fenton finds that practitioners often obtain total IgE or allergen-specific IgE (sIgE) blood tests without realizing that abnormally high IgE levels or the presence of sIgE are not solely diagnostic of food allergy but mean only that the patient has been sensitized to the allergen -- and they are not necessarily evidence of clinical disease.

Intradermal testing, total serum IgE, or atopy patch tests are not recommended in the diagnosis of food allergy, either alone or in combination.[2] "These tests are easy to do, and might point to a food allergy, but they don't give a definitive diagnosis," explained Dr. Fenton. Some methods, such as skin prick test and sIgE can assist in identifying the causative food in a patient with confirmed food allergy. Food elimination diets or food/symptom diaries, although evidence for usefulness is lacking, may have a role in confirming food allergy when an oral food challenge is not practical.
The Oral Food Challenge

"The gold standard test for diagnosis of food allergy is the oral food challenge," continued Dr. Fenton. "But many primary care providers will be reluctant to do an oral food challenge, if they've never done one before. It has some level of risk and should be performed only by someone with experience, and in the appropriate setting. General practitioners can be trained to do the oral food challenge, but they need to have the right equipment and support -- epinephrine on hand to treat anaphylaxis and easy access to an inpatient facility if a transfer is required."

Oral food challenges are recommended to cut down on misdiagnosis of food allergy. The double-blind, placebo-controlled food challenge (DBPCFC) is the most specific test for diagnosing food allergy, but this test can be expensive and inconvenient to administer outside of research. Therefore, the guidelines state that single-blind and open-food challenges may be used in the clinical setting.[2] A negative oral food challenge rules out food allergy, whereas a positive oral challenge supported by medical history and laboratory tests is diagnostic of food allergy. Patients should be advised not to attempt an oral food challenge on their own -- it must be designed and performed under medical supervision to document the dose that provokes the reaction and to administer symptomatic treatment, which may require management of anaphylaxis. The dose, timing, and escalation must be carefully controlled. Practitioners who aren't comfortable conducting oral food challenges should refer these patients to allergy specialists.
Multiple Allergies

With more than 170 foods capable of causing IgE-mediated reactions, pinpointing a patient's trigger can be onerous. Prior to initiating an oral food challenge, suspected foods are eliminated from the diet for 2 to 8 weeks. When multiple allergies are suspected, all foods in question must be strictly avoided simultaneously.[2] During the oral food challenge, ingestion of each food is separated by a break of about 2 hours.[4] Depending on the number of suspect foods, it might be necessary to conduct the food challenges in multiple sessions.