Patch tests with house dust mite antigens in atopic dermatitis patients: methodological problems

Patch tests with house dust mite allergens were performed in 21 atopic dermatitis patients with a positive prick test and RAST for house dust mite. Variables in methodology of patch testing, i.e. allergen concentration, application time, and intensity of tape stripping, were studied. Tests were performed with Dermatophagoides pteronyssinus solutions containing 20X, 100X and 500X the prick test concentration and purified HDM antigen: 10 and 50 micrograms/ml P1Ag solution. The series was applied on 8X or 15X tape-stripped and clinically normal skin on the back during 24 and 48 h. Non-specific reactions due to tape stripping, fixation tape or patch test occlusion were frequently observed: after 15X tape-stripping in 3/7 (24-h application) and 6/7 (48-h application) patients, after 8X tape-stripping in 2/19 (24-h application) and 8/19 (48-h application) patients. Reactions clinically assessed as specific occurred in 6/21 (29%) atopic dermatitis patients, 4/6 occurring in the 10 patients with a serum IgE greater than 1000 kU/l. High allergen concentrations and 48 h of application increased the number of patients with specific reactions. If 15X tape-stripping had been omitted, 2/3 patients tested in this manner and showing specific test reactions would have been negative. Further conclusions regarding the value and the preferable method of patch testing with atopic allergens require an in vitro control test.