Specific serum IgE in the diagnosis of egg and milk allergy in adults

Levels of specific serum IgE to cow's milk, whole hen's egg, egg white, and egg yolk were compared to the outcome of double-blind, placebo-controlled food challenge (DBPCFC) with fresh egg and/or milk in 21 adults with a case history of immediate hypersensitivity to egg and/or milk. Specific serum IgE was measured by four different commercially available tests and by an inhouse Maxisorp RAST using freshly prepared food extracts. Sensitivities and negative predictive accuracies were generally high with egg white and milk, but low with egg yolk. Specificities and positive predictive accuracies were low for all allergens and tests. Changing the cutoff levels did not improve the ability of the tests to predict clinical allergy. Among commercially available test allergens, egg white gave the most consistent results in levels and class scores, and the highest degree of concordance with DBPCFC, whereas egg yolk and milk varied more. Applying freshly prepared food extracts in Maxisorp RAST did not improve diagnostic value. Measuring specific serum IgE levels in control subjects tolerant to egg/milk showed that false positive reactions occurred frequently among patients with another food allergy and atopic dermatitis, whereas most tests were likely to be negative in pollen-allergic and nonallergic volunteers. In conclusion, specific IgE measurements with egg white and milk were useful for exclusion of symptomatic hypersensitivity to egg and milk in patients with a positive history, whereas DBPCFC is still mandatory in patients with positive history and positive test. Measuring egg-yolk-specific IgE or using freshly prepared food extracts for specific IgE measurements added no further diagnostic information. The rate of clinically insignificant positive test results seems to be influenced by the prevalence of other food allergies and/or atopic dermatitis in the population under study.