Skin testing and food challenges for the evaluation of food allergy

Skin testing by prick technique has an excellent safety record in the evaluation of food hypersensitivity. Skin prick tests for the common food allergens are excellent tools for identifying those at very low risk of reaction on eating the food but are of variable value in identifying patients who will be positive on challenge. Intradermal skin tests to foods are less safe and appear to add no predictive information. Skin tests to less common food allergens, especially fruits, are less well characterized and may require use of the food item itself as the source of allergen rather than a commercial extract. For a few foods, the CAP system fluorescent enzyme immunoassay (Pharmacia, Peapack, NJ) recently has been shown to have good ability to identify patients at very high probability of reaction on oral challenge. Oral challenge remains the definitive method of demonstrating sensitivity or tolerance to a food. The double-blind, placebo-controlled food challenge is the gold standard of diagnosis, but in many situations, simpler open or single-blind challenge procedures may be substituted. With careful, incremental dosing and a low starting dose, oral challenges for food hypersensitivity have an excellent safety record. Skin prick tests are of little value in the evaluation of adverse food reactions not mediated by IgE. Oral challenge is relied upon in this situation for definitive diagnosis, but challenges may be cumbersome if the time course of the presumed reaction is not rapid.