Patch testing remains the gold standard in the diagnosis of allergic contact dermatitis. Patches used in testing consist of a wide spectrum of allergens, with variability in the stability of products over time. Due to limited allergen stability, careful storage and preparation is needed to prevent product degradation over time. Expiration dates are provided by manufacturers to ensure stability and reactivity, while minimizing the risk of product degradation contributing to inaccurate testing results. Preparation of patch series can be time intensive and procurement of allergens comes with an associated economic burden. Expired allergens are not routinely used in patch testing, however many clinics have expired allergens accessible. There is paucity of evidence comparing the reactivity of expired vs non-expired patch series. If expired allergens remain effective, this could result in significant cost-savings and accessibility implications for dermatology practice.
Adults (age 18 years or older) referred for patch testing.
Relative or absolute contraindication to patch testing
Wide spread dermatitis prior to patch placement
Inability to return to clinic for reading of results
Patient non-consenting
Single group
Patch 1 (Expired)
Biological/VaccineAll enrolled participants will be simultaneously patch tested with both expired and non-expired patches. Therefore, there is no difference in intervention amongst study participants.
Patch 2 (non-expired)
Biological/VaccineAll enrolled participants will be simultaneously patch tested with both expired and non-expired patches. Therefore, there is no difference in intervention amongst study participants.
Patch Testing Response (Positive/Negative) Concordance Rate (%) Between Non-Expired and Expired Allergens
Each allergen will be graded on response using a standard patch test scale including: irritant reaction \['IR'\], '+/-' for doubtful, '+' for erythema and infiltration, '++' for edematous or vesicular and '+++' for spreading, bullous or ulcerative response that will be graded by the participating Dermatologist. Reactions graded '+', "++", or "+++" are consider a positive result. Concordance rate will be expressed as a percentage (%) between tested allergens that were non-expired and that were expired (i.e. Nickel sulfate hexahydrate was found to have a 92% concordance rate, meaning that in 92% of cases, the Nickel allergen in the non-expired and expired patches were both found to both be either positive or negative while in 8% of cases the response differed per the scale listed above.)
Reaction/Morphology Scoring Concordance (%)
For each positive allergen, severity (i.e. '+/-', '+', '++', "+++") and morphology (i.e. erythema, infiltration, edematous, vesicular, bullous, ulcerated) will be recorded. Concordance rate will be expressed as a percentage (%) between tested allergens that were non-expired and that were expired (i.e. Nickel sulfate hexahydrate was found to have a 92% concordance rate, meaning that in 70% of cases, the Nickel allergen in the non-expired and expired patches were both found to have the exact same severity and morphology, while in 30% of cases the severity and/or morphology differed per the scale listed above.)
Stability Concordance (%) Amongst Mediums
Each allergen is suspended within a medium, either petrolatum or aqueous solution. Not only will concordance (%) of positive and negative reactions be assessed amongst allergens and compared between non-expired and expired, but also between mediums to determine if there is a difference in stability over time amongst mediums used to determine if particular mediums result in degradation over time.
Irritant Reaction Rates (%)
Final patch reading will score reactions on a standarized scale, with irritant reaction representing a negative reaction. However, we will compare rates and concordance (%) of irritant reactions between allergens to determine if their is reproducibility, or if expired allergens result in differing rates of irritant reactions. (i.e. Nickel sulfate allergen was shown to have a 50% increased rate of irritant reactions between the expired to non-expired allergens, meaning that Nickel resulted in an irritant reaction in 6 cases of the expired Nickel and 4 cases of the non-expired Nickel, suggesting that expired Nickel allergens may become more irritating over time, resulting in more irritant reactions.
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