Patch testing: need for local guidelines

Patch testing is a simple procedure performed in order to identify allergens in allergic contact dermatitis. Currently at Teaching Hospital, Ragama we use test material battery of European Environmental and Contact Dermatitis Research Group (EEC-DRG) standard and we also maintain a database.

A retrospective analysis of patch test data of past two years (01.01.2007 - 31.12.2008) was done. The commonest type of dermatitis referred for patch testing was foot dermatitis (28.1%), followed by hand dermatitis (77.4%). The commonest pre-patch testing suspected allergen was rubber products (31.4%) followed by cement (14%) and hair dye (8.9%).

There was a significant number of negative tests (45.5% of total). Out of positive results the commonest allergen was potassium dichromate (27.3%) followed by mercaptobenzothiazole 24.2%). 56.8% of positive results correlated positively with suspected pre-patch test allergen.

Certain allergen such as quatemium 15 has never given positive results in our group.

Positivity rates are lower, and the pattern of positive allergens differs compared to European results.

These findings prompt the need of multicenter analysis of patch test data in order to formulate local guidelines.