Health Articles

The diagnosis of food allergy requires a careful history, physical examination, selective skin or serum IgE antibody tests in cases of suspected IgE-mediated disorders, appropriate exclusion diets, and sometimes blinded provocation challenges. At present, there is no evidence of the diagnostic utility for the following assays: quantitation of food-specific serum IgG or IgG4 antibodies, serum food antigen-antibody complex assays, cytotoxic food testing, tests of lymphocyte activation (proliferation, interleukin-2, or leukocyte inhibitory factor studies), or sublingual or intracutaneous neutralization or provocation.
Once food allergy or hypersensitivity has been diagnosed definitively, the only proven form of therapy is strict elimination of the offending food. This requires considerable time (and ideally a dietitian) to educate the patient on spotting all forms of “hidden foods” and assuring a nutritionally sound diet. Teaching patients to read food labels is necessary to ensure good compliance with an elimination diet. About Affective Disorders.
Patients who have IgE-mediated food allergies also must be prepared to treat accidental ingestions; this includes using injectable epinephrine and oral liquid antihistamines. In addition, patients must be prepared to go to the nearest emergency facility for further treatment when indicated.
The role of breastfeeding and food allergen avoidance in the prevention of atopy and food allergy remains controversial. However, it appears that breastfeeding (especially when the mother avoids major allergens – milk, egg, peanut, fish – during lactation) and/or the use of hydrolyzed infant formulas can prevent some atopic dermatitis and food allergy in high-risk infants, but whether it actually prevents respiratory allergy is not yet clear.

In the practice setting, an open or single-blind oral food challenge may be used to screen for allergic reactions to food. However, in cases in which multiple food allergies are diagnosed, positive responses should be confirmed by double-blind, placebo-controlled food challenges (DBPCFCs). DBPCFCs are the gold standard for diagnosing food allergies and have been used successfully in both children and adults for examining a variety of food-related complaints. The choice of foods used in DBPCFCs is based on history, skin test (or serum IgE antibody) results, or foods suspected on the basis of elimination diets. DBPCFC testing should be performed by a specialist or an experienced clinician; it is not a procedure suited for most primary care practices. (For details see Bock 1988 in Suggested Readings.)
Diagnosis of nonIgE-mediated food hypersensitivity such as malabsorption syndromes and eosinophilic gastroenteritis is facilitated by endoscopy and intestinal biopsy prior to and after the child is placed on an elimination diet. In the malabsorption syndromes, villous atrophy may be partial or complete and often is patchy. Consequently, multiple biopsies may be required to exclude this diagnosis, especially in young children. IgA antigliadin and IgA antiendomysial antibodies can be measured to screen for celiac disease.
However, this diagnosis depends on demonstrating biopsy evidence of villous atrophy and inflammatory infiltrate while the patient is ingesting gluten, resolution of biopsy findings after 6 to 12 weeks of gluten elimination, and recurrence of biopsy changes following reinstitution of gluten.
Food-induced enterocolitis and colitis syndromes may require an oral food challenge in the office or hospital. A positive challenge will provoke occult or grossly apparent blood in the stools, an increase in stool neutrophils and eosinophils over baseline, and an increase in the total peripheral blood neutrophil count of 3500 cells/mm³ over baseline at 6 to 8 hours after the challenge.

Several gastrointestinal immune-mediated disorders have been described. Food-induced enterocolitis, generally associated with ingestion of cow milk or soy-based formula, has its onset between 1 week and 3 months of age, with vomiting and diarrhea severe enough to produce dehydration. Stools contain gross or occult blood and often are watery and positive for carbohydrate (reducing substances). When diarrhea contains gross or occult blood only and pathology is limited to the distal bowel, the condition is defined as food-induced colitis. Both syndromes improve within 72 hours of eliminating the allergen. Malabsorption syndromes have been described secondary to ingestion of cow milk, soy-based products, egg, and wheat. These patients have patchy intestinal villous atrophy when biopsied. The more extensive malabsorption enteropathy with total villous atrophy (often called celiac syndrome) is associated with sensitivity to gliadin, a component of gluten. Allergic eosinophilic gastroenteropathy syndrome can affect children and presents with postprandial nausea, vomiting, abdominal pain, diarrhea, and steatorrhea. Affected patients may have elevated serum IgE levels, positive skin tests, peripheral eosinophilia, iron deficiency anemia, hypoalbuminemia, and a specific food allergy.

The natural history of food allergy in children varies from patient to patient, and food allergies are not always life-long. Studies have shown loss of gastrointestinal food allergy in 1 to 3 years among one third of children, even though results of skin tests and RASTs may not change. The likelihood of losing a food allergy depends on the food that provokes the symptoms and the degree to which the patient maintains the allergen elimination diet. Allergy to peanuts, tree nuts, and fish and seafood appear to be more long-lasting than allergy to milk,soy, and egg.

Ingestant or Food Allergy

The evaluation of the child who is suspected of having a food allergy can be fraught with unnecessary confusion because of misuse of terms. It is important to define the clinical syndrome to enhance understanding of the medical problem. An adverse food reaction is a generic term used to describe any untoward reaction following the ingestion of a food or food additive. Adverse food reactions can be categorized into food allergy (food hypersensitivity) or food intolerance. A food allergy is an abnormal immunologic response. A food intolerance is due to a nonimmunologic mechanism, such as toxins contained in the food, metabolic disorders (eg, disaccharidase deficiencies), or idiosyncratic reactions. Lactose intolerance due to lactase deficiency, a common cause of cow milk intolerance, often is mislabeled as milk allergy.

In addition, patients may experience a nonimmune adverse reaction to a constituent in food, such as monosodium gluconate added to food during processing, spices such as peppers (capsacian) added as flavoring during cooking, or preservatives. Although food additives, such as coloring or preservatives, may induce urticaria and, rarely, systemic allergy, the hypothesis that they contribute to behavior problems such as hyperactivity or other entities such as learning disabilities has never been substantiated in well-designed and controlled studies.

Symptoms other than those of the gastrointestinal system can result from allergic reactions to food. Anaphylactic reactions, fatal and near-fatal, have been reported both in children and adults. Anaphylactic shock associated with exercise following ingestion of certain foods has been reported in individuals, even though neither food nor exercise alone induced anaphylaxis. Ingestion or contact with food is a common cause of acute urticaria or angioedema. Chronic (>6 weeks’ duration) urticaria secondary to food allergy is much less common. Atopic dermatitis in infants and children commonly is associated with food allergy, especially from eggs, milk, wheat, peanuts, and fish.

Within 10 to 60 minutes after ingestion of a food allergen, some children may develop a pruritic, erythematous morbilliform rash. It has been postulated that repeated ingestion of the offending allergen leads to continuation of the IgE inflammatory response, which provokes the pruritus, scratching, and development of eczematous lesions of atopic dermatitis. Although not common, both upper and lower respiratory tract symptoms also have been described secondary to food allergy; however, respiratory symptoms associated with food allergy in the absence of gastrointestinal or skin symptoms is unusual.
Allergies articles