Oral Allergy Syndrome - Diagnosis

Diagnosis

The patient typically already has a history of atopy and an atopic family history. Eczema, otolaryngeal symptoms of hay fever or asthma will often dominate leading to the food allergy being unsuspected. Often well-cooked, canned, pasteurized or frozen food offenders cause little to no reaction due to denaturation of the cross-reacting proteins, causing delay and confusion in diagnosis as the symptoms are elicited only to the raw or fully ripened fresh foods. Correct diagnosis of the allergen type/s involved is critical. OAS sufferers may be allergic to more than just pollen. Oral reactions to food are often mistakenly self-diagnosed by patients as caused by pesticides or other contaminants. Other reactions to food—such as lactose intolerance and intolerances which result from a patient being unable to metabolize naturally occurring chemicals (e.g., salicylates and proteins) in food—need to be distinguished from the systemic symptoms of OAS.

The cornerstone of diagnosis remains an accurate history of symptoms and an elimination diet followed by a food challenge. Skin prick testing and RAST testing are used as adjuncts to the clinical history—they cannot be used for diagnosis alone. Prick to prick testing with fresh foods is more reliable for some extremely labile allergens such as those found in apple than testing with commercial extracts which will commonly give a false negative. If the history is suggestive and the skin prick test negative, fresh foods should be used.