From the Guidelines
Patch testing panels include the North American Standard Series, the European Standard Series, and the T.R.U.E. Test, as well as supplemental panels such as the Cosmetic Series, Corticosteroid Series, Dental Series, Metal Series, Shoe Series, and Textile Series, which are applied to the patient's back for 48 hours and read at 48,72, and sometimes 96 hours 1.
Patch Testing Panels
The choice of panel depends on the patient's exposure history and suspected allergens. The standard method involves the application of antigen to the skin at standardized concentrations in an appropriate vehicle and under occlusion, with the back being the most commonly used site due to convenience and area availability 1.
- The North American Standard Series contains 50 common allergens like nickel, fragrances, and preservatives.
- The European Standard Series has similar allergens but with regional variations.
- The T.R.U.E. Test is a commercially available panel with 35 allergens on ready-to-use patches.
Application and Reading
These panels are applied to the patient's back for 48 hours, then read at 48,72, and sometimes 96 hours, with reactions graded from negative to extreme positive (+3) 1.
- The standard method involves the application of antigen to the skin at standardized concentrations in an appropriate vehicle and under occlusion.
- Various application systems are available, with Finn chambers being the most commonly used.
Importance of Patch Testing
Patch testing helps identify specific contact allergens causing dermatitis, allowing patients to avoid these substances and manage their condition effectively, with a sensitivity and specificity of between 70% and 80% 1.
- The British Society for Cutaneous Allergy (BSCA) revises its baseline series regularly to remove allergens that diminish in relevance and add important emerging allergens.
- Supplemental series are also recommended to target less common allergens such as fragrances or rubber chemicals.
From the Research
Patch Testing Panels
The panels used for patch testing vary, but most include a standard series of allergens.
- A study by 2 used a standard series of 60 allergens, while the North American Contact Dermatitis Group (NACDG) used a series of 50 allergens during the same period.
- Another study by 3 mentions that patch test systems can be a comprehensive panel (70-80 allergens) or targeted and limited to a more common allergen series (35 allergens).
- The NACDG patch test results from 2019-2020, as reported by 4, used a screening series of 80 allergens.
- A retrospective review by 5 compared the North American screening series with a limited series, such as the Thin-Layer Rapid-Use Epicutaneous (T.R.U.E.) Test, and found that the extended panel increased sensitivity.
- The most recent NACDG patch test results from 2021-2022, as reported by 6, also used a screening series of 80 allergens.
Common Allergens
The most commonly positive allergens vary, but some common ones include:
- Nickel sulfate hexahydrate, as reported by 2, 4, and 6
- Methylisothiazolinone (MI), as reported by 4 and 6
- Fragrance mix, as reported by 2 and 4
- Hydroperoxides of linalool, as reported by 4 and 6
- Cobalt chloride, as reported by 2 and 6
Panel Marks
There is no specific information on the marks used for patch testing panels, but the results are typically measured and interpreted based on the presence and severity of reactions to the allergens.
- A study by 3 mentions that measurement and interpretation of the test results require training and experience, as well as consideration of relevance and clinical history.