Prevalence of IgE antibodies specific for food allergens in patients with chronic urticaria of unexplained etiology.

We investigated whether some cases of chronic urticaria of unexplained cause might be related to food allergy which had remained undetected during routine examination. This investigation was undertaken as the consequence of the availability of a new in vitro assay for specific IgE with increased sensitivity. The following three groups of subjects were studied: 1) a control group of 60 nonatopic subjects, 2) 60 patients with allergy to perennial aeroallergens without skin involvement, and 3) 60 patients suffering from chronic urticaria with no evidence of any triggering factor despite careful clinical investigation. Specific IgE against 19 food allergens frequently involved in urticaria were investigated in all subjects with the new CAP System (Pharmacia). Positive results (CAP > 0.70 kU/l) for one or more food allergens were found in none of the nonatopic controls, in six of the subjects with respiratory allergy, and in 16 of the urticaria patients. The use of an in vitro test with an increased sensitivity allowed us to detect a significant prevalence of IgE specific for food allergens in patients with chronic urticaria of unknown origin. This suggests that, in several of those patients, chronic urticaria might be triggered by a food allergy undetected by the usual methods.