ATOPY PATCH TEST WITH DIFFERENT VEHICLES AND ALLERGEN CONCENTRATIONS - AN APPROACH TO STANDARDIZATION

Background: In some patients with atopic eczema, eczematous skin lesio ns can be induced by patch testing with aeroallergens. Methods: To est ablish a standardized system for the atopy patch tet (APT), 36 patient s with atopic eczema, four patients with rhinoconjunctivitis and 10 he althy control subjects were epicutaneously tested with allergen extrac ts from house dust mite, cat dander, and grass pollen. APTs were perfo rmed on nonabraded, uninvolved skin with 1000 and 10,000 protein nitro gens units (PNU)/gm allergen in petrolatum or hydrogel. Reactions were evaluated after 48 and 72 hours and compared with skin prick and spec ific serum IgE (CAP-RAST; Pharmacia, Uppsala, Sweden). Results: After 48 hours, 57 clear-cut positive reactions with eczematous, often folli cle-bound, appearance were diagnosed from a total of 432 test sites. S eventy-two percent of these positive reactions in patients with atopic eczema developed with 10,000 PNU/gm and 28% with 1000 PNU/gm. Sixty-s even percent of reactions were elicited with allergens in petrolatum v ersus 33% when hydrogel was used as vehicle. Allergen-specific concord ances of APT (10,000 PNU/gm, petrolatum) ranged from 0.39 to 0.53 (pri ck tet) and 0.42 to 0.69 (CAP-RAST). In healthy control subjects and p atients with rhinoconjunctivitis without atopic eczema, no clear-cut p ositive APT reaction was seen. Conclusions: Petrolatum as vehicle and an allergen concentration higher than 1000 PNU/gm may lead to improved APT results on unchanged skin. In the future, the clinical relevance of an IgE-mediated sensitization for eczematous skin lesions may be ev aluated by the APT.