Patch Testing with the Swedish Baseline Series in Two Countries

Patch testing is a very effective mean to investigate causes of allergic contact dermatitis (ACD), but results obtained in different countries is usually hard to compare due to reading of patch tests. The aim of the study was to examine the prevalence of contact allergy to substances present in the Swedish baseline series and to compare results between the clinics in Vilnius and Sweden when the patch test procedure is similar in both countries. Consecutive patients with suspected ACD were tested with the Swedish baseline series at the university hospitals in Malmö, Sweden, and Vilnius, Lithuania in the years 2010–2012. Positive patch test reactions to at least one allergen was observed in 115 (53.7%) in Lithuania and in 237 (55.4%) in Sweden. The top 5 most frequent allergens (and respective prevalence rates) in Lithuania were as follows: nickel sulphate (25.7%), methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) (10.3%), cobalt chloride (7.5%), potassium dichromate (6.1%), formaldehyde (6.1%). The most prevalent positive patch tests reactions in Sweden were to nickel sulphate (18.9%), cobalt chloride (6.3%), M. pereirae resin (5.6%), MCI/MI (4.9%), Amerchol L 101 (4%). Statistically relevant differences were seen in sensitization to preservatives (3.7% in Lithuania and 1.8% in Sweden, p<0.001) and metals (13.1% in Lithuania and 9.3% in Sweden, p<0.03). In conclusion, this multicenter study provides some information on the prevalence of contact allergy to the most common contact allergens in two countries, although it is not possible to establish if the different prevalence was due to the difference in atopic background or allergen exposure. This should be further investigated.