What should be considered during epicutaneous patch testing?

Indications for epicutaneous patch testing include the detection or exclusion of allergic contact dermatitis of the skin, transitional mucosa or oral mucosa, suspected delayed-type immune reactions to ingredients of implants, and certain drug reactions (maculopapular exanthema, symmetrical drug-related intertriginous and flexural exanthema [SDRIFE], acute generalized exanthematous pustulosis [AGEP], and fixed drug eruption). When available, allergen preparations that have been pharmaceutically tested and that are approved or marketable as medicinal products should be used. Existing diagnostic gaps can be closed by testing the patient’s own materials in a suitable preparation. Interferences of ultraviolet (UV) light exposure or drugs with patch test reactions have to be considered. In addition to the reading after 48 h and 72 h, a further reading between day 7 (168 h) and day 10 (240 h) is useful, since about 15% of the positive test reactions remain undetected without this late reading. All positive patch test reactions considered allergic must be evaluated with regard to their clinical relevance based on existing exposures.