Diagnosis of Allergy

The desire for simple, office or laboratory test for allergy is easy to understand, but difficult to fulfill. No single test will ever reveal the complex and variable nature of allergic reactivity. The lack of specific tests for different kinds of allergy have hindered progress in this field.

Skin tests are best used to diagnose airborne allergens which cause hay fever.  There is a convenient correlation between nose-reactive IgE and skin-reactive IgE . By introducing tiny amounts of suspected antigens into the skin, a local wheal and flare reaction, similar to a mosquito bite, is produced if reactive IgE is present on skin mast cells.

The association of hay fever and some asthma, and skin tests with allergy practice was further confirmed by the relative success of "allergy shots". These shots came to characterize the allergist's office; other aspects of allergy practice often were neglected.

 Allergy shots are immunological treatments. The immune response to any reactive substance can be modified by giving repeated challenges of the reactive substances.

Serum assays of IgE antibodies are also useful in diagnosing type 1 food allergy. In a study of patients with asthma, and atopic dermatitis, plasma histamine and tryptase levels rose in the group with immediate reactions to food challenges. An elevated plasma tryptase level is thought to indicate mast cell activation. The authors noted subjects who had delayed symptoms - diarrhea at 4 hours, erythema and urticaria and 8 hours, and exacerbation of atopic dermatitis at 24 hours had slow or low histamine responses with no tryptase elevation.

The idea that standardize protein extracts of foods would be the most reliable and "scientific" tests for food allergy have been thwarted by observations that skin tests with fresh-extracts from food correlated better with symptoms on challenge testing. Food antigens can be complex, multiple, and may not survive processing into standardized extracts. In a review of studies of type 1 reactions to vegetables and fruit, mouth and tongue symptoms dominated. Systemic reactions included urticaria, angioedema, asthma, rhinitis, headaches, and itchy hands. Testing with commercial food-protein extracts was found less reliable than using the fresh food.

Skin tests do not reveal the more complex forms of food allergy. Some labs offer other tests for food allergy, including IgG RAST, and immune complex assays. While these tests produce interesting results, they are expensive and do not answer the main question - what should the patient eat?

The difficulty in diagnosing food allergy and other food-related problems in clinical medicine and disputes within the allergy community have left many patients suffering, frustrated and confused. At the same time as physicians default in the diagnosis and treatment of food-related illnesses, many non-medical practitioners have launched careers in the food and chemical "sensitivity" business, using diverse, sometimes curious and bizarre methods, dubious tests and questionable treatments. Even well-intentioned efforts to diagnose and treat food allergy are often based on faulty premises and fail to deliver proper results.

Food allergy is diagnosed by physicians who understand the multisystem, polysymptomatic patterns of illness involved. These patterns are revealed by a careful history, and the diagnosis made on clinical grounds. The pattern of food-related illness, the sequence of symptom production, and the distribution of disturbances in the body can be explained if complex causation is assumed. Without a well-equipped research laboratory it will not be possible to actually measure the pathophysiological events.

 See Diet Revision as Diagnosis.