Novel Approaches to Food Allergy
Diagnosis of Food Allergy
University Children's Hospital
The most common foods leading to IgE-mediated allergic reactions are cow's milk, hen's egg, wheat, soy, and peanut and tree nuts. The diagnostic work-up of food allergy includes a thorough medical history, in vitro tests (e.g. specific serum IgE), in vivo tests (e.g. skin prick test, atopy patch test), and oral challenges (preferably performed as double-blind, placebo-controlled food challenges).
Decision points have been established by some groups for a couple of allergens, allowing us to make oral food challenges superfluous in cases where the cut-off value exceeds the 95% or 99% predicted probability. However, these values vary considerably among populations studied and have to be established for each allergen separately. Our data indicate that specific IgE decision points can be calculated for hen's egg (95% = 12.6 kU/l, 99% = 59.2 kU/l), but not for cow's milk, wheat or soy.
Skin prick test decision points can be calculated in the same way. Our study resulted in values of 13.0 mm (95%) and 17.8 mm (99%) for hens' egg, and 12.5 mm (95%) and 17.3 mm (99%) for cow's milk. Infants tend to have slightly lower levels compared to older children.
The atopy patch test, an epicutaneous test performed with native foods, provides the best specificity and positive predictive values as a single test. The combination of the atopy patch test together with the skin prick test or specific serum IgE enhances the efficiency of each single test.
Around 10% of positive oral food challenges are not IgE-mediated. Therefore, the suspicion of food-related symptoms, rather than proof of specific IgE, should be the indication to perform oral challenges.
The time point of the diagnostic work-up seems to determine, which parameter may be helpful: while all mentioned parameters add information to determine which patient should receive an elimination diet, only oral food challenges are currently meaningful to decide whether a patient has become tolerant after a time of avoidance.
In the daily practice, no oral food challenge is required in the case of a suggestive history of an anaphylactic reaction, if specific serum IgE or the skin prick test value is above the decision point, or if the patient suffers from a clear oral allergy syndrome induced by pollen associated food allergens. Open challenges may be justified in cases of questionable anaphylaxis or immediate type clinical reactions. Double-blind, placebo-controlled food challenges are recommended if late phase clinical reactions are suspected or the patient complains on subjective symptoms.