Current patch test results in consecutive patients with, and chemical analysis of, disperse blue (DB) 106, DB 124, and the mix of DB 106 and 124.

Disperse blue (DB) 106 and 124 are important textile dye allergens. However, the dye raw material is impure, leading to uncertainty regarding the actual patch test (PT) concentration. To examine, (i) the allergen content of previously and currently used DB 106 and 124 and a respective mix, and (ii) the frequency of positive PT reactions to the DB 106/124 mix and to the single compounds in consecutive PT patients. High performance liquid chromatography (HPLC) analysis and purification of DB 106 and 124, respectively. Descriptive analysis of PT data from the Information network of departments of dermatology obtained between January 2003 and December 2005. Retrospectively, 2 batches of the DB 106/124 mix proved to contain an amount of allergen different to the 1 declared (based on information of suppliers of raw material). However, since February 2005, DB 106 and 124, respectively, are available at a reliable concentration of 0.3% petrolatum. In 2005, the prevalence of positive PT reactions to both the mix (0.89%) and the single constituents combined (0.56%) did not qualify them for inclusion in the standard series. Quality control, providing accurate test concentrations of allergens based on technical grade purity raw materials is necessary for valid diagnosis of contact allergy and comparable epidemiological data.

Patch testing with p-toluene diamine preparations of different ages.

Analyses of the stability of 1% p-toluene diamine (PTD) in petrolatum used for patch testing showed a rapid decline of the PTD concentration down to 0.1%, possibly due to the generation of dye complexes. To study whether the diagnostic quality of this test preparation is compromised by the chemical reactions taken place, a multicentre study was conducted by the German Contact Dermatitis Research Group (DKG), comparing patch test results in 177 patients with simultaneously tested PTD preparations of different ages. During the 10-month course of this study, the age of the batches ranged from 2 to 11 months for batch A, from 7 to 16 months for batch B and from 11 to 20 months for batch C. There were no statistically significant differences between reactions to batches A and B, A and C, and B and C. Agreement of patch test reactions to the 3 batches was very good and comparable to the general reproducibility of patch test with standard allergens. The chemical reactions mentioned above apparently do not affect the diagnostic quality of PTD patch test preparations because the true allergen probably is not PTD itself, but one or more of the reaction products.