Author: Aamenah Al-Ani, Medical Student, University of Auckland, New Zealand. DermNet New Zealand Editor-in-Chief: A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. February 2018.
The classical tests for immediate Type 1 hypersensitivity (allergy) are specific IgE antibody levels, such as the radioallergosorbent test (RAST), and skin prick tests. Although often performed in patients with asthma and hay fever, these tests are not applicable to atopic dermatitis, which is not caused by a Type 1 reaction. However, the same allergens may also cause Type IV or delayed hypersensitivity reactions.
An atopy patch test is an epicutaneous patch test with the type 1 allergens known to elicit IgE-mediated hypersensitivity reactions. Eczematous skin lesions, if any, are evaluated after 24–72 hours. Atopy patch tests can be used as a diagnostic tool in patients with atopic dermatitis triggered by aeroallergens or by food allergy [1,2].
Positive atopy patch tests are associated with allergen-specific T-lymphocyte responses.
The indications for atopy patch tests in a patient with atopic dermatitis include:
Allergens are applied directly onto clinically uninvolved and untreated skin of the back. They remain in place for 48 hours. Tape stripping should be avoided .
The most common allergens tested in atopy patch tests are:
The European Task Force on Atopic Dermatitis (ETFAD) study in six European countries showed that the allergen that most often elicited a positive atopy patch test reaction was house dust mite extract, followed by pollen allergens .
Various vehicles have been used to carry the allergen: petrolatum, hydrogel and no vehicle. Allergens in petrolatum generally elicit more positive atopy patch test reactions than allergens in a hydrophilic vehicle .
Evaluation of the sites is conducted after 48 and 72 hours. The ETFAD grading system may be used.
There is no “gold standard” for atopy patch tests. Positive results may correlate with a history of allergen-specific flares of dermatitis.
When compared with classic tests of IgE-mediated hypersensitivity:
The atopy patch test does not replace the classic methods of diagnosis of IgE-mediated allergy .
Predictors of positive atopy patch test reactions include:
See the DermNet NZ bookstore.
© 2018 DermNet New Zealand Trust.
DermNet NZ does not provide an online consultation service. If you have any concerns with your skin or its treatment, see a dermatologist for advice.