Are double-blind food challenges necessary before starting an elimination diet?

Food allergy is normally treated by eliminating the offending food. Such a measure, however, may cause nutritional and sociopsychological problems, so an allergy must be diagnosed with the utmost certainty. To date the most reliable diagnostic test is the double-blind food challenge (DBFC). The rationale for using this test is the marked difference in positive results with open and double-blind food challenges. Only about 30% of open challenges that appear positive are confirmed on blind challenge. There is ample evidence, too, that a negative DBFC may in fact indicate tolerance to that food. From the literature it appears that almost all patients who reintroduced a certain food into their diet after a DBFC had given negative findings did not present any adverse reaction to it. In our caselist of 21 patients with probable reactions to foods but negative DBFC, 19 (90.5%) tolerated the "incriminated" food well when it was reintroduced into their diet even in unlimited amounts. Only two (9.5%) again presented symptoms when they started taking large amounts of the problem food. Therefore, one precaution recommended before reintroducing a food item into a patient's diet after a negative DBFC is to check how it is tolerated at high doses. A review of the literature confirms the unquestioned utility of the DBFC. Nevertheless, in some situations this test is not indicated. The main one, of course, is in patients with life-threatening symptoms such as anaphylactic shock or glottis edema, in whom any provocation test is contraindicated.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of the elimination diet in adults with food allergy.

The aim of the study was to check whether, after a period of complete exclusion of the offending foods in adult subjects suffering from food allergy, these foods could subsequently be safely reintroduced into the diet. Patients with chronic urticaria and/or perennial rhinitis negative for secondary pathology or other allergies were subjected to a strict diagnostic protocol for food allergy. Briefly, out of a case list of 207 patients, we found 23 patients whose symptoms were clearly related, on open reintroduction, to at least one food. The really offending foods in these patients were subsequently identified by double-blind, placebo-controlled food challenges. Only 10 of the 23 patients had positive challenges for 13 foods. Double-blind challenges were repeated after 1 year or more of avoidance of the offending foods to evaluate the persistence or disappearance of sensitivity. We found that five (38%) of the 13 previously offending foods were well tolerated. Thus, in adults, as previously proved in children, dietary avoidance of the offending foods appears to be an effective measure for dealing with food allergy. The kind of foods involved and the completeness of their avoidance appeared to be important factors favoring the reestablishment of tolerance in adults.

IgE-mediated food allergy.

The behaviour of some immunologic parameters was studied in order to explain the presence or the lack of symptomatology in subjects with IgE specific to foods. In particular, we compared the levels of serum and salivary IgA and IgE antibody specific to apple in 33 patients allergic to birch and with anti-apple IgE, of whom 24 had oral allergy syndrome after eating apple and nine were apple tolerants. We found no differences in the IgE-related parameters such as levels of anti-apple IgE antibody in serum and secretions, mean size of apple skin prick test, and number of patients with a positive histamine release from peripheral basophils stimulated by apple. Similarly, we detected no statistically significant differences in serum and salivary total IgG and total anti-apple IgA antibody of the two groups. We could, however, observe a significantly higher anti-apple salivary IgA/anti-apple serum IgE and anti-apple salivary IgA/anti-apple serum IgA ratios and a significant correlation between the same parameters in tolerant patients when compared with the intolerants. These results seem to suggest that the presence of appropriate levels of secretory anti-apple IgA associated to anti-apple IgE might be one of the factors playing a key role in the prevention of clinical symptoms in atopic subjects.