Approach to suspected food allergy in atopic dermatitis. Guideline of the Task Force on Food Allergy of the German Society of Allergology and Clinical Immunology (DGAKI) and the Medical Association of German Allergologists (ADA) and the German Society of Pediatric Allergology (GPA).

The following guideline of the "Arbeitsgruppe Nahrungsmittelallergie der DGAKI" (Task Force on Food Allergy of the German Society of Allergology and Clinical Immunology) and the ADA ("Arzteverband Deutscher Allergologen", Medical Association of German Allergologists) and the GPA (German Society of Pediatric Allergology) summarizes the approach to be taken when food allergy is suspected in patients with atopic dermatitis (neurodermatitis, atopic eczema). The problem is clinically relevant because many patients assume that allergic reactions against foods are responsible for triggering or worsening their eczema. It is important to identify those patients who will benefit from an elimination diet but also to avoid unnecessary diets. Elimination diets (especially in early childhood) are associated with the risk of malnutrition and additional emotional stress for the patients. The gold standard for the diagnosis of food-dependent reactions is to perform placebo-controlled, double-blind oral food challenges because specific IgE, prick tests and history often do not correlate with clinical reactivity. This is particularly true in the case of delayed eczematous skin reactions. Diagnostic elimination diets should be used before an oral provocation test. If multiple sensitizations against foods are discovered in a patient, an oligoallergenic diet and a subsequent stepwise supplementation of the nutrition should be performed. If a specific food is suspected of triggering food allergy, oral provocation should be performed after a diagnostic elimination diet. As eczema-tous skin reactions may develop slowly (i. e. within one or two day), the skin be inspected the day after the provocation test and that a repetitive test be performed if the patient has not reacted to a given food on the first day of oral provocation. The guideline discusses various clinical situations for patients with atopic dermatitis to facilitate differentiated diagnostic procedures.

Diagnostic approach for suspected pseudoallergic reaction to food ingredients.

Chronic urticaria, recurrent angioedema and non-allergic asthma have all been associated with pseudoallergic reactions to food ingredients. For atopic dermatitis and diseases of the gastrointestinal tract, this association is controversial. Pseudoallergic reactions can be elicited by additives as well as by natural food ingredients. An altered histamine metabolism may be associated with pseudoallergy. Acute urticaria or a short episode of angioedema is not an indication for exhaustive evaluation. If basic diagnostic screening is negative in chronic urticaria, a low-pseudoallergen diet can be considered. Skin and serological tests are not objective diagnostic parameters for pseudoallergic reactions. The severity of symptoms should be documented while the patient is on a low-pseudoaller-gen diet. Oral provocation with additives leads to reproducible symptoms only in a few cases. Therefore, if a low-pseudoallergen diet brings improvement, the patient is then exposed to a pseudoallergen-rich "super meal". After a positive reaction to the "super meal" the challenge with additives takes place in the form of collective group exposition. When the patient has asthma or a history of anaphylac-toid reactions, testing with individual substances in carefully increasing dosages is required. The suspicion of adverse reactions against histamine can be confirmed by a challenge with histamine dihydrochloride. In the case of respiratory symptoms, provocation by inhalation should be considered. Objectifying symptoms especially in gastrointestinal diseases is mandatory and should include double-blind placebo-controlled food challenge, if possible.

Skin testing with food allergens. Guideline of the German Society of Allergology and Clinical Immunology (DGAKI), the Physicians' Association of German Allergologists (ADA) and the Society of Pediatric Allergology (GPA) together with the Swiss Society of Allergology.

Skin testing has a central role in the diagnosis of food allergy. Prick testing is well- established as a routine diagnostic tool. Nonetheless, unstable allergens and the lack of standardized extracts create difficulties in the identification of sensitization to foods in patients with suspected food allergy. Therefore prick-to-prick tests with native (raw, fresh) foods are still recommended. The indications and contraindications are the same as those of routine skin testing in clinical allergology. We recommend a careful and restricted application of skin tests in patients with a history of severe anaphylaxis to foods.