Diagnosis of food allergies and intolerances in the study of prophylaxis and control groups in infants.

There is no definitive way to distinguish a true atopic IgE-mediated sign or symptom due to food from an intolerance reaction due to irritation, enzyme deficiency or other idiosyncratic cause. The presence of IgE-specific antibody against a food as demonstrated by an immediate wheal and flare skin test reaction or a positive RAST is presumptive evidence of a cause and effect relationship. The younger the patient, the more likely a positive RAST or skin test is to be significantly causally related to the illness. Nevertheless, in almost 100 infants at 4 months of age, five were observed to have both a positive skin test and a positive RAST to a food, with only two having any detectable allergic illness. This observation in a prospective study of the value of a prophylaxis regimen in the prevention or amelioration of atopic allergic disease in infancy, underlines the problem of the ascertainment of allergy. The problem is even greater when the suspected allergen is a food, for a positive laboratory test does not rule it in nor a negative test rule it out. Thus, the diagnosis of food allergy is dependent on a careful history, physical examination, elimination diets, food challenges and the cautious interpretation of skin tests and laboratory tests including a total serum IgE level and RAST. Under ordinary circumstances an individual with complaints, signs and symptoms of allergic disease consults the physician to help find the cause of the illness.(ABSTRACT TRUNCATED AT 250 WORDS)