- Bruce A Brod, MD
Bruce A Brod, MD
- Clinical Professor of Dermatology
- University of Pennsylvania School of Medicine
Patch testing is an essential investigation to identify specific allergens in allergic contact dermatitis (ACD) or, in some cases, to make the diagnosis of ACD. Patch testing is based upon the principle that in sensitized individuals, primed antigen-specific T lymphocytes of the Th1 phenotype circulate throughout the body and are able to recreate a delayed-type hypersensitivity reaction when nonirritating concentrations of the antigen are applied to normal skin.
This topic will discuss indications, techniques, and interpretation of patch testing. The basic mechanisms, clinical manifestations, diagnosis, and management of ACD are discussed separately. (See "Basic mechanisms and pathophysiology of allergic contact dermatitis" and "Clinical features and diagnosis of allergic contact dermatitis" and "Management of allergic contact dermatitis".)
INDICATIONS FOR PATCH TESTING
Indications for patch testing may include:
●Persistent eczematous eruptions when contact allergy is suspected 
●Any chronic dermatitis, especially when involving the hands, feet, face, or eyelids
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- INDICATIONS FOR PATCH TESTING
- SELECTION OF ALLERGENS
- Standard (baseline) series of allergens
- Additional series of patch testing
- Individualized patch testing
- PATCH TEST PROCEDURE
- Preparing the patient
- - Effect of systemic immunosuppression
- - Effect of oral antihistamines
- - Effect of ultraviolet radiation
- Patch test site
- Types of tests
- - Closed test
- - Open test
- - Semi-open test
- - Repeated open application test
- - Usage test
- Patch test reading
- - Initial reading
- - Second reading
- PATCH TEST INTERPRETATION
- DETERMINING THE CLINICAL RELEVANCE
- COMPLICATIONS OF PATCH TESTING
- Active sensitization
- The "angry back"