An allergy refers to an exaggerated reaction by our immune system
in response to bodily contact with certain foreign substances. When an
allergen comes in contact with the body, it causes the immune system to
develop an allergic reaction in persons who are allergic to it.
Ten to 20% of adults in the population report food intolerances—mostly they refer to these as "food allergies." But only a small proportion of these are genuine, immunologically mediated allergies. Food
intolerances are therefore overrated on the one hand, but on the other hand, potentially dangerous food allergies are often not diagnosed at all or only with delays.
This study focused on the diagnosis of immunoglobulin E (IgE) mediated food allergy (type I allergy). Any mention of food allergy therefore always refers to IgE mediated food allergy.
From January 2000 to December 2007, all persons in whom food allergies were suspected were examined in a standardized fashion with stepwise allergological diagnostics. The tests were intended to provide answers to two questions: Were the symptoms caused by food? If yes, which foods were responsible? The selection and interpretation of the diagnostic methods depend on the symptoms (anaphylaxis or oral allergy syndrome) and the food under suspicion (known or rare allergen).
To identify a suspected food, the type, amount, preparation, and individual ingredients of a meal were investigated, as were the packet declarations of ready meals. Mere assumptions were made about so-called hidden allergens—e.g., cow's milk or egg in sausages or ready meals; seasonings, soya, or nuts in baked products or sweets. Particularly indicative of an allergy were reproducible symptoms—i.e., similar symptoms after an earlier or subsequent repeated exposure. The history was completed with questions about known allergies and the manifestations of atopy.
Laboratory tests
Food specific IgE in the serum was measured with a commercially available immunoassay. The test method binds IgE antibodies in the serum to solid phase bound food allergens. A positive test shows values up to 100 kU/L. Food specific IgE was measured only in a targeted way and not used as a search test. In patients with positive skin reactions to common and known food allergens and in oral allergy syndrome, no IgE measurements were taken.
Skin tests
Conducting and reading skin prick tests on the volar lower arm after 20 minutes was done in accordance with international guidelines (10). In the prick-to-prick test with native foods, the prick test lancet was first pricked into the food and then into the skin. Grain flours, nut flours, or seasonings were floated with physiological.
Neither a positive skin prick test nor a finding of food specific IgE is always clinically relevant; they only indicate sensitization.
419 patients aged 10 to 85 years (median 40 years) were studied, 270 (64.4%) were female and 149 (35.6%) male.
35.3% of patients had isolated skin symptoms. Symptoms of anaphylaxis (table) were reported in 35.8%— with or without skin symptoms, the airways were affected.
In 214 patients (51.1%), IgE mediated food allergies were diagnosed, supported by unequivocal findings;
however, stepwise allergological diagnostic tests ruled out food allergies in 205 patients (48.9%) (figure 4).
The authors identified food allergens in their own patients by using standardized diagnostic tests and thereby enabled beneficial allergen avoidance. In many cases, however, it was of equal importance to rule out food allergies and therefore prevent unnecessary diets and imposing limitations on people's everyday lives.
An allergy to cow's milk or eggs is common in children but rare in adults. Recurrent anaphylaxis often occurs when people eat in restaurants or at fast food venues, because the ingredients are unknown or not fully declared (25). Most patients who died as a result of anaphylaxis knew about their food allergy and had identified the causative allergen.
