Comparative detection rates and concordance of the TRUE test and the European baseline series in allergic contact dermatitis: a prospective head-to-head study

Abstract Allergic contact dermatitis (ACD) is a common inflammatory skin condition in which accurate identification of causative allergens is essential for targeted avoidance and long-term control. Patch testing is the diagnostic gold standard, and both the TRUE Test and the European Baseline Series (EBS) are widely used in clinical practice, but they differ in allergen composition and practical implementation, which may influence detection rates and concordance. A prospective, within-patient, head-to-head study was conducted in 100 consecutive patients with suspected ACD at Meir Medical Center, a tertiary referral center in Israel, between January 2018 and June 2019, to compare detection rates and concordance between the TRUE Test and the EBS rather than formal diagnostic accuracy, sensitivity, or specificity. All participants underwent simultaneous patch testing with the TRUE Test and the EBS, enabling direct paired comparison while minimizing inter-patient variability. Patch test reactions were read at 48 and 72 h, and positive reactions were recorded. Concordance between the two systems for shared allergens was categorized as high (≥ 80%), moderate (40–<80%), or low (< 40%). Because clinical relevance was not systematically assessed, findings are reported as detection rates and agreement between test systems. Overall, 50 patients exhibited at least one positive reaction. A total of 72 positive reactions were identified, with 56 detected by the EBS and 53 by the TRUE Test. For allergens included in both systems, the overall concordance rate was 58.7%. High concordance was observed for common allergens, including nickel sulfate, fragrance mix, and cobalt chloride. Moderate concordance was found for p-phenylenediamine and Balsam of Peru, whereas low or no concordance was noted for methylchloroisothiazolinone/methylisothiazolinone (MCI/MI), Caine Mix III/Caine mix, and potassium dichromate. In addition, system-unique allergens contributed positive reactions, indicating that discrepancies may be influenced by differences in allergen panels, although differences in formulation, concentration, vehicle, or intrinsic test characteristics cannot be excluded. In conclusion, the TRUE Test and the EBS showed broadly comparable detection rates and agreement in this cohort, supporting their complementary rather than interchangeable use. Patch testing strategies should balance standardization and practicality with flexibility for individual exposure histories and evolving allergen profiles.