New Guidelines Issued for Food Allergies

New Guidelines Issued for Food Allergies News Author: Laurie Barclay, MD

In children of parents with asthma, the rate of observed food allergy may be 4 times higher than in the general population. IgE-mediated food reactions may occur as a result of gastrointestinal sensitization, respiratory tract sensitization, or sensitization through the epidermis. Immune responses include acute IgE-mediated, local inhalational, systemic, and cell-mediated reactions (eg, atopic dermatitis and celiac disease). Sensitivity to most food allergens, such as milk, wheat, and egg, tend to remit in late childhood. Sensitivity to peanut, tree nuts (walnuts, cashew, Brazil nut, pistachio), and seafood are likely to continue throughout life. Allergies to fruits and vegetables tend to develop later in life as a consequence of shared homologous proteins with airborne allergens (eg, pollen). Anaphylaxis after exposure to foods reflects reactions of respiratory, dermatologic, cardiovascular, and other organ systems. In children, anaphylaxis occurs most commonly after ingestion of peanuts, other legumes, tree nuts, fish, shellfish, milk, and eggs. Diagnosis requires a detailed history of exposures and targeted physical examination. Initial evaluation may include skin prick or puncture tests. Commercial food extracts with stable proteins (eg, peanut, milk, egg, tree nuts, fish, shellfish) are reliable to detect IgE antibodies in most patients. Extracts from foods with more labile proteins (eg, many fruits and vegetables) are less reliable for diagnosis. Intradermal skin tests are not recommended as they are dangerous. A positive skin test has a positive predictive value (PPV) of less than 50% (ie, not specific) but a negative skin test has a negative predictive value (NPV) of more than 95% (ie, highly sensitive) and can reliably rule out IgE-mediated food allergy. Double-blind, placebo-controlled food challenge is most likely to provide a high PPV in conjunction with a careful history. In vitro serum tests are useful in patients with a history of life-threatening reaction, with medical conditions, a nonreactive histamine control, and in pregnant women. If a patient has a history of anaphylactic reaction with a positive test for IgE specific antibodies, no further evaluation is usually required. Provocation-neutralization is considered disproved as a diagnostic method. Hair analysis, food-specific IgG, cytotoxic tests, and immune complex assays are considered experimental or unproven. Adverse reactions to food additives (such as tartrazine) are rare.
Monosodium glutamate is a rare cause of angioedema, urticaria, or bronchospasm in patients with asthma. Sulfites produce bronchospasm in 5% of the population with asthma. Food allergy prevention strategies include breast-feeding, maternal dietary restriction during breast-feeding, late introduction of solids and allergenic foods, and the use of hypoallergenic infant formulas although effectiveness of the strategies has not been established. Avoidance of allergens is the key management strategy. Because elimination diets may lead to malnutrition or other serious adverse effects (eg, personality change), every effort should be made to ensure that the dietary needs of the patient are met and that the patient and/or caregiver(s) are fully educated in dietary management measures to prevent inadvertent exposure to known or suspected allergens. Injectable epinephrine should be given to patients or caregivers of patients with a history of IgE-mediated systemic reactions. Delay in epinephrine administration is the most common cause of fatalities, with peanuts and tree nuts accounting for most fatal and near-fatal reactions.