Diagnostisches Vorgehen bei Verdacht auf eine pseudoallergische Reaktion durch Nahrungsmittelinhaltsstoffe

Chronic urticaria, recurrent angioedema and non-allergic asthma may be due to pseudoallergic reactions to food ingredients. For atopic dermatitis and gastrointestinal symptoms the role of these non-allergic reactions is discussed controversially. Pseudoallergic reactions can be elicited by food additives as well as naturally occurring food components. An altered histamine metabolism may be associated with pseudoallergy. Extensive diagnostic measures are not indicated for an acute urticaria or a short episode of angioedema. Only when symptoms become chronic or at least intermittent, basic diagnostic measures are justified. If this procedure is unsuccessful, pseudoallergy to food components should be considered as a causative factor. In order to confirm this suspicion, patients should adhere to a low pseudoallergen diet for 3 weeks. During this period, a daily documentation of symptoms is recommended. As the underlying pathomechanism is not IgE-mediated, skin and blood tests are not useful for diagnosis. After apparent improvement or remission of symptoms, the causative role of a low pseudoallergen diet can be proven by re-exposure to foods rich in pseudoallergens over 2 days. As food additives only play a minor role in pseudoallergic reactions, a mixture of relevant food additives can be given at one time in most patients. Patients with asthma bronchiale or a history of anaphylactoid reactions should be challenged with single food additives in increasing doses. If adverse reactions to histamine are suspected, an oral provocation with histamine dihydrochloride is recommended. For patients with respiratory symptoms inhalant challenge tests are suggested. Double-blind, placebo-controlled food challenge is recommended if the patient suffers from gastrointestinal symptoms only and pseudoallergy is suspected.