Patch Test Preparations: Basis and State-of-the-Art Modern Diagnostic Tools for Contact Allergy

Reliable quality of epicutaneous patch test (PT) preparations is a prerequisite for establishing a robust diagnosis in patients with suspected allergic contact dermatitis due to delayed-type sensitization. It is difficult to identify potential quality issues in daily practice, since confirmatory methods are lacking and assessment of PT-relevance is predominantly based on patients' history and exposure. The quality of PT products can be affected, e.g., by the properties of the active substance, an insufficient development of the PT preparation or issues during manufacturing. Resulting quality deficiencies can cause both false-negative and false-positive test results. As PT preparations are medicinal products according to Directive 2001/83/EC, they require a marketing authorization (MA) entailing assessment of quality, safety and efficacy by the competent authorities. The corresponding product dossier is the basis for MA. It is continuously updated, e.g., upon change of a source material supplier, ensuring comparability of the respective product over time. Compliance with regulatory requirements is a crucial foundation for sustainable quality to prevent product deficiencies, ensuring reliable test results in practice. Harmonization across the EU is important to ensure the widespread availability of high-quality PT products. This review presents the MA requirements of PT preparations in the EU, as well as challenges previously reported by physicians.