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Careful history aimed at defining the type of reaction at the time of onset of symptoms related to food ingestion, suspect food, and related allergens are of key importance. If a food allergy is suspected, allergy food skin testing and to a lesser extent blood food testing (ImmunoCAP) may afford some help in identifying potentially allergic foods. Allergy food testing, however, needs to be interpreted properly. For example, up to 50% of all positive food skin test may not represent clinically significant food allergies. In some cases, there is enough allergy antibodies to produce a positive skin or blood test but not enough to produce an allergic reaction when eating that food. Other immune defense mechanisms may also be at play that prevents the absorption of allergic proteins from the gut that prevent allergic reactions expressing themselves. In other cases, the skin test or ImmunoCAP blood test remains positive in an individual who has lost symptomatic allergy to a food that can now be eaten without reaction. On the other hand, if an allergy food skin test is negative, it is unlikely that the food can produce an allergic food reaction. Blood food allergy testing (ImmunoCAP) is generally less reliable in this way with many more false negative tests being observed.
To determine whether a positive food skin or blood test is clinically significant, several approaches may be taken including avoidance diets and/or food challenges in an allergist’s office. A food challenge consists of an individual eating the suspect food under observation. Food challenges should be done under a physician’s guidance and never performed in the home environment. They should only be done in an office that is equipped to treat severe allergic reactions, typically in a board-certified allergist and immunologist’s office. The other use of challenge testing is to decide whether an individual has outgrown a particular food allergy. Unconventional food testing through blood cytotoxic tests, sublingual food challenges, food neutralization shots, basophil histamine release, applied Kinesiology, blood allergen specific IgG4 measurement, electrodermal testing, and acupuncture testing have no scientific merit and therefore cannot be relied on for accurate diagnosis and/or treatment and are generally not paid for through medical insurance, including Medicare.
Food allergies may present with gastrointestinal symptoms. Aside from the patient’s history, allergy skin tests, lab studies, and elimination diets, additional x-rays, and/or gastrointestinal/endoscopic exams with biopsy may be necessary to make a correct diagnosis of a food allergy or a disease process mimicking a food allergy. A biopsy of the GI mucosa in patients with chronic non-IgE-mediated food reactions is often observed to contain infiltrations of eosinophils, a known atopic marker of allergic inflammation. These abnormalities can be seen throughout the G2 tract from the esophagus through to the large colon.
Non-IgE-mediated food reactions
Less frequently encountered adverse reactions to foods are immunologically induced reaction to foods that may be due to non-IgE antibodies or sensitized T-cells or other cells responding to an immunological reaction to an ingested food. Such reactions occur hours or days after ingesting a food and symptoms tend to be localized to the gastrointestinal tract.
1. Food protein induced enterocolitis syndrome (FPIES)
This condition may occur in formula-fed infants by 4-6 months of age, and is usually due to cow’s milk or soy. Symptoms include severe vomiting and diarrhea within hours of eating the offending food antigen. Allergy testing is usually negative. Avoidance is the best treatment. Food challenges may be helpful to establish a safe point to reintroduce these foods.
2. Food-induced colitis
Food-induced colitis, also called allergic colitis, usually appears by 6 months of age. Symptoms include loose stools, bloody stools, despite the infant’s healthy appearance. Allergy tests are negative. Using casein hydolysate formulas, and in some cases, amino acid-based formulas, cures symptoms.
3. Celiac disease
This condition results from small intestinal mucosal injury in response to ingestion of gluten-containing grain, especially wheat, rye, and barley. Patients complain of abdominal cramps, nausea, bloating, diarrhea, and weight loss. Biopsy reveals a flattening of the mucosa, cellular infiltrate of the lamina propria, and IgA antibodies against the reticulum and smooth muscle endomysium. Lab studies include anti-endomysial Ab (IgA); anti-gliadin antibody (IgA) and anti-transglutaminase antibody (IgA; IgG).
4. Eosinophilic esophagitis
This is an inflammatory condition in which the inner layers of the esophagus are infiltrated with eosinophils and associated with symptoms os dyphagia (difficulty swallowing), heartburn and chest discomfort. In children, symptoms can also include nausea, vomiting and abdominal pain. Although the cause is unclear, food allergy is suspected in some cases. Allergy testing can help and may indicate the need for a trial on an elimination diet. In addition to eliminating the suspected food, dilation of the esophagus, and swallowing fluticasone proprionate (Flovent) or budesonide (Pulmicort), inhaled steroids used in asthma treatment may be helpful. When acid reflux complicates eosinophillic esophagitis, proton pump inhibitors are added to the treatment program and are often tried first before swallowed inhaled steroids.
5. Dermatitis herpetiformis
A cutaneous manifestation of gluten sensitivity, dermatitis herpetiformis usually occurs in children ages 2-7 years. The rash is an erythematous pruritic rash mostly over the knees, elbows, shoulders, buttock, and scalp. Many of these patients have Celiac disease. Treatment consists of elimination of gluten from the diet.
Food Induced Anaphylaxis
For individuals, especially young children with food induced anaphylaxis, oral desensitization to the culprit food may be possible. Most allergic foods for desensitization are under clinical trials and still in research and therefore not safe for the general population. In the unique circumstance of peanut allergy in a very young infant 4-11 months of age, may be skin tested for peanut allergy and undergo peanut oral challenges before going on a peanut containing diet which prevents onset of peanut allergy. Individuals with food induced anaphylaxis should also have access to an epinephrine auto injector.
For more information on food reactions and allergies, visit our Get Relief: Food Reactions.