Frequency of false positive responses in patients with multiple positive reactions in patch test

Background and aim: Contact dermatitis is an inflammatory skin response due to contact with environmental materials manifested as acute or chronic eczema. Patch test is the standard test to recognize responsible allergen. The objective of this study was to evaluate the frequency of false positive patch test responses in patients with Exited Skin Syndrome (ESS).Materials and methods: Fourteen patients older than 12 years with allergic contact dermatitis who had more than one positive reaction in first patch test were re-tested with the same allergens at the time of remission of their eczema. The patches were removed after 48 hours and responses read according to ICDRG guidelines.Results: The patients included 5 men and 9 women with a mean age of 34.92 years. The most common allergens in first patch test were: nickel sulfate (10), cobalt chloride (5), colophony (4), potassium dichromate, PTBF, fragrance mix and MCI/MI (3 each). In the repeated test, the most common positive responses were: nickel (10), cobalt and colophony (4 each), potassium dichromate and fragrance mix (3 each). In 6 of 14 patients the results of second test was different from first one. Three of these patients had active eczema at the time of first test, which in 2 of them one positive response and in one of them, 2 positive responses became negative in second test.Conclusion: It is recommended that patch test be repeated after a while in patients with multiple positive reactions in first test, particularly after remission of active eczema.