An update on the performance of the <scp>Australian Baseline Series</scp> in detecting allergic contact dermatitis

Patch testing is the gold standard for the diagnosis of allergic contact dermatitis (ACD).1 The baseline or standard series refers to a minimum set of allergens used for patch testing every patient and should reflect the most common allergens in a given population.2 The Australian Baseline Series (ABS) was inaugurated by our group in 2012 to include the 60 most common and pertinent allergens in our patient population. It is updated every 3 years to make sure this is still the case. The aim of this study was to evaluate the efficacy of testing with the current ABS in order to diagnose ACD. We conducted a retrospective study of 1129 patients who were patch tested at our centre from 1 January 2021 to 31 December 2023. Of these patients, 246 (23.7%) were given a final diagnosis of ACD. Patients with at least one relevant positive reaction were divided into three groups: (i) reactions only to allergens in the ABSs; (ii) reactions to allergens in the ABS and to additional allergens; and (iii) reactions only to allergens not present in the ABS. The ABS alone was successful in detecting the cause of ACD in 62.2% (153/246) of patients (Table 1). In 26.2% (62/246), the ABS detected at least one relevant allergen, but there were also relevant allergens outside of the ABS (Table 1). In 12.6% (31/246), no relevant allergens were detected in the ABS, but allergens were detected in additional series or by testing patients' own products (Table 1). The most frequent relevant reactions to allergens in the ABS that fully diagnosed ACD included hydroperoxides of limonene/linalool, methylisothiazolinone (MI), fragrance mix 1 and methylchloroisothiazolinone/MI (Table 2). The most frequently occurring allergens not included in the ABS were decyl glucoside, lavender absolute, cetrimonium bromide, lemongrass oil, p-aminophenol and tetraethylthiuram disulphide (Table 3). 153 (62.2) Work related: 36 (23.5%) 62 (25.2) Work related: 10 (6.2%) 31 (12.6) Work related: 4 (12.9%) These results are on par with our last review of the ABS in 2020.3 This indicates that we have maintained our diagnostic accuracy by continuing to review and update our series with relevant allergens to our population. The ABS will be updated at the end of 2024 with the replacement of sesquiterpene lactone mix and betamethasone-17-valerate with decyl glucose and lavender absolute. The addition of decyl glucoside is mirrored in the European Baseline Series4 and is recognised as a common cosmetic hapten within North America.5 The ABS remains an acceptable screening tool for identifying patients with ACD. However, it must be emphasised that using the ABS alone, has the potential to miss a relevant reaction in up to one third of cases. It is particularly important to test patients to additional series as well as patient's own products to obtain a higher yield of reactions, and ultimately a more accurate diagnosis. James Fuller: Writing – original draft; writing – review and editing; data curation. Amanda Palmer: Data curation. Rosemary Nixon: Conceptualization; writing – review and editing. The authors declare no conflicts of interest.