Atopy patch test with different vehicles and allergen concentrations: An approach to standardization

Background: In some patients with atopic eczema, eczematous skin lesions can be induced by patch testing with aeroallergens. Methods: To establish a standardized system for the atopy patch test (APT), 36 patients with atopic eczema, four patients with rhinoconjunctivitis and 10 healthy control subjects were epicutaneously tested with allergen extracts from house dust mite, cat dander, and grass pollen. APTs were performed on nonabraded, uninvolved skin with 1000 and 10,000 protein nitrogen units (PNU)/gm allergen in petrolatum or hydrogel. Reactions were evaluated after 48 and 72 hours and compared with skin prick and specific serum IgE (CAP-RAST; Pharmacia, Uppsala, Sweden). Results: After 48 hours, 57 clear-cut positive reactions with eczematous, often follicle-bound, appearance were diagnosed from a total of 432 test sites. Seventy-two percent of these positive reactions in patients with atopic eczema developed with 10,000 PNU/gm and 28% with 1000 PNU/gm. Sixty-seven percent of reactions were elicited with allergens in petrolatum versus 33% when hydrogel was used as vehicle. Allergen-specific concordances of APT (10,000 PNU/gm, petrolatum) ranged from 0.39 to 0.53 (prick test) and 0.42 to 0.69 (CAP-RAST). In healthy control subjects and patients with rhinoconjunctivitis without atopic eczema, no clear-cut positive 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 evaluated by the APT. (J ALLERGY CLIN IMMUNOL 1995;95:677-84.).