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Treatment of Food Allergies Reviewed Print E-mail
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พฤหัสบดี, 28 พฤษภาคม 2009
June 23, 2008 — The double-blind, placebo-controlled food challenge remains the most specific test to confirm the diagnosis of food allergies, according a review published in the June 15 issue of the American Family Physician. Food allergy is the leading cause of nondrug-related anaphylaxis."Food allergies affect 4 to 5 percent of children and 2 to 3 percent of adults, yet false attribution of symptoms to food allergy remains a problem," write Kurt Kurowski, MD, from the Chicago Medical School at Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, and Robert W. Boxer, MD, from Rush North Shore Medical Center in Skokie, Illinois. "Population-based studies of children and adolescents have shown that only 10 percent of those who believe they have food allergy can be proven to have one. Disorders associated with food allergy, such as eosinophilic esophagitis, are being increasingly recognized, and some other previously known disorders, such as gastroesophageal reflux disease in infants, are being increasingly attributed to food allergies." Although family practitioners are of key importance in recognizing and diagnosing immunoglobulin E (IgE)–mediated food allergies, they must also play a vital role in orchestrating an appropriate workup for symptoms that patients falsely attribute to allergies.Any food is a potential allergen, but in children, more than 90% of acute systemic reactions to food, including anaphylactic reactions, result from allergy to eggs, milk, soy, wheat, or peanuts. In adults, the most frequent offenders are crustaceans, tree nuts, peanuts, or fish.The most common manifestation of food allergy is the oral allergy syndrome, with transient symptoms that are limited to the mouth and throat.For the diagnosis of food allergy, skin-prick and radioallergosorbent tests (RAST) for specific foods are approximately 85% sensitive and 30% to 60% specific. Because intradermal testing has a higher false-positive rate as well as a higher risk for adverse reactions, it should not be used for the initial evaluation of food allergy. The most specific test to confirm the diagnosis is still the double-blind, placebo-controlled food challenge.The mainstay of treatment of food allergy involves recognizing and avoiding the responsible food. In the event of accidental exposure, patients who experience anaphylactic reactions need to be prepared with emergent intramuscular epinephrine and instruction in self-administration. For more minor allergic reactions to food, antihistamines may be helpful.Food challenge testing and the elimination diet, in which suspected allergens are avoided, may have both a diagnostic and therapeutic role. The double-blind, placebo-controlled food challenge is helpful in older children and adults who have atypical reactions or reported reactions to foods that are seldom implicated in allergy.Although the double-blind, placebo-controlled food challenge is still the most specific test for confirming diagnosis, false-positive and false-negative rates are still 5% or more. If the challenge is not designed correctly, the results may be erroneous. Furthermore, reactions occurring days later may cloud interpretation. Other disadvantages of the double-blind, placebo-controlled food challenge are that it is time consuming, poorly tolerated by patients, and usually unnecessary for diagnosis.When there is higher pretest suspicion of true food allergy, the single-blind food challenge may be useful in older children and adults with atypical reactions or reported reactions to foods that are seldom implicated. Blinding of patients decreases patient bias, and this test is technically easier to perform than the double-blind food challenge.The open food challenge can be used to test multiple suspected foods, which are given with masking foods, followed by blinded food challenges for positive reactions. This test is technically the easiest to perform, but it is more prone to patient bias.The elimination diet may be used for patients of any age. If there is clinical suspicion that more than 1 food may be causing allergy, multiple foods can be eliminated from the diet. To confirm the diagnosis in patients who improve while avoiding certain foods, the elimination diet is usually followed by food challenge. This approach is typically well tolerated by patients. To ensure that the diet is nutritionally adequate once certain foods are eliminated, dietitian consultation is usually required, and the diet is maintained until the symptoms markedly decrease while the patient is free of significant medications.Symptoms of anaphylaxis may include gastrointestinal tract symptoms such as abdominal pain, cramping, diarrhea, or vomiting; and respiratory tract symptoms including chest tightness, cough, dyspnea, wheezing, or rhinorrhea. Generalized allergic symptoms may include angioedema, flushing, generalized urticaria, pruritus, feeling of impending doom, hypotension, shock, metallic taste in the mouth, and throat swelling.If anaphylaxis is suspected, epinephrine should be administered urgently. If symptoms do not completely resolve with epinephrine alone, intramuscular diphenhydramine, systemic corticosteroids, and histamine H2 blockers can be added. Supplemental oxygen should be given for bronchospasm or laryngeal edema.Patients who have had even a single anaphylactic reaction to food should be prescribed 2 age-appropriate epinephrine pens and a medical identification bracelet providing information about their allergy, be instructed in how to use the pens, and be followed up to make sure they know the proper technique for injection. Most patients in whom a second phase of anaphylaxis develops should be observed in a hospital.Specific recommendations for clinical practice, and their accompanying level of evidence rating, are as follows:
  • When clinical suspicion for food allergy is high, IgE testing with skin prick or a RAST is appropriate for diagnosis (level of evidence, C).
  • Patients (or their caregivers) who have known or suspected anaphylactic reactions to specific foods should carry injectable epinephrine at all times and be instructed with regard to its use (level of evidence, C). This recommendation was made in a guideline based on consensus opinion of the Joint Task Force on Practice Parameters.
  • Compared with cow's milk–based formulas, there is some evidence that hydrolyzed formulas reduce infant and childhood allergies. However, there is no evidence to support the use of hydrolyzed formula to breast-feeding (level of evidence, B).
To prevent food allergies, the American College of Allergy, Asthma and Immunology recommends that infants with a family history of 2 primary relatives with an atopic disease be exclusively breast-fed for the first 6 months, with continued breast-feeding through at least the first year and solid food not being introduced until after 6 months of age."Because approximately one half of all women are secretors (what they ingest will appear in their breast milk), the breastfeeding mother should avoid eggs, milk, tree nuts, peanuts, and seafood," the reviewers write. "In the child's diet, nuts, shellfish, and fish are delayed until three to four years of age."The review authors have disclosed no relevant financial relationships. Am Fam Physician. 2008;77:1678-1686, 1687-1688.
Clinical Context
According to Roehr and colleagues in the 2004 issue of Clinical and Experimental Allergy, the prevalence of food allergy is 4% to 5% in children and 2% to 3% in adults, although of the children who believe they have a food allergy, only 10% have a confirmed diagnosis.Sampson reported in the May 1999 issue of the Journal of Allergy and Clinical Immunology that children might have a higher prevalence of food allergy because of their relatively immature mucosal gut barrier and immune response to doses of food antigens that are present in the intestines.
Study Highlights
  • More than 90% of all food allergies are from egg, milk, soy, wheat, and peanuts in children and crustaceans, tree nuts, peanut, and fish in adults.
  • History consistent with food allergy are reaction within minutes to hours of ingestion; similar reactions after ingestion of the same food; lack of other causes; suspected high-risk food; onset in young child; and personal or family history of atopic dermatitis, asthma, allergic rhinitis, or food allergies.
  • Food allergy is outgrown by 70% of children with egg allergy, 85% with milk allergy, and only 20% with peanut allergy.
  • Of children with food allergies, asthma will develop in 40% to 60% and allergic rhinitis in 30% to 55%.
  • Differential diagnosis includes carcinoid syndrome, celiac disease, giardiasis, gustatory rhinitis, irritable bowel disease, lactase deficiency, scombroid poisoning, and sulfite ingestion.
  • Anaphylactic symptoms are abdominal pain, cramping, diarrhea, vomiting, angioedema, flushing, generalized urticaria, pruritus, chest tightness, cough, dyspnea, wheezing, feeling of impending doom, hypotension, shock, metallic taste in mouth, rhinorrhea, throat swelling, and uterine contractions.
  • Risk factors for anaphylaxis-related death are new onset in adults; persistent allergies in adolescents; asthma; allergies to crustaceans, tree nuts, peanuts, or fish; and delay in epinephrine treatment.
  • Food-dependent, exercise-induced anaphylaxis is a rare condition occurring in patients who exercise within 6 hours of ingesting the food antigen, most commonly wheat.
  • Food allergy accounts for 30% of acute urticaria and 3% to 4% of chronic urticaria.
  • 35% of atopic dermatitis is from food allergy, especially to eggs, milk, and peanuts.
  • The most common food allergy is the oral allergy syndrome:
    • Swelling and pruritus of the lip, tongue, throat, and palate occur when foods that cross react with airborne allergens contact the oropharynx: birch pollen (fresh fruit, carrots, celery, hazelnuts, parsnips, potatoes), grass pollen (kiwi, tomato), and ragweed pollen (bananas, melons).
  • Most children with allergic eosinophilic gastrointestinal tract disorders will improve on a hydrolyzed formula or amino acid–based diet.
  • Patients with symptoms suggesting IgE-mediated food allergy should undergo skin-prick testing or RAST:
    • Skin-prick test has 85% sensitivity and 30% to 60% specificity.
    • RAST has similar sensitivity and 50% specificity.
    • Tests not recommended initially are intradermal and patch tests.
  • Patients with anaphylactic reactions to common food antigens and confirmatory IgE testing do not need food challenge tests.
  • Patients with clinically suspected food allergy and negative IgE testing should undergo food challenge testing.
  • The most specific test for confirming food allergy is a double-blind, placebo-controlled food challenge.
  • Management of anaphylaxis includes urgent epinephrine and, if needed, diphenhydramine, ranitidine, corticosteroids, and oxygen.
  • In infants with family history of atopic disease, measures to postpone food allergy are breast-feeding exclusively for first 6 months and continued through first year; solid food introduction after age 6 months; avoidance of eggs, milk, tree nuts, peanuts, and seafood in the breast-feeding mother; and avoidance of nuts, shellfish, and fish until the child is age 3 to 4 years.
  • Hydrolyzed formula vs cow's milk formula might prevent allergies, but no evidence exists that hydrolyzed formula might reduce allergies vs breast milk.
  • Future research will assess specific oral tolerance induction, monoclonal IgG, and Chinese herbal tea.
Pearls for Practice
  • For patients with suspected IgE-mediated food allergy, the recommended skin prick and RAST are 85% sensitive and 30% to 60% specific, whereas the double-blind, placebo-controlled food challenge is the most specific test to confirm food allergy.
  • Management of food allergies includes avoidance of food that caused the reaction and treatment of anaphylaxis with epinephrine, diphenhydramine, ranitidine, and systemic corticosteroids.
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