Patch testing by additional series of allergens: results of further experiences.

Background: Patch testing with additional series (AS) of allergens may be a useful tool in diagnosing allergic contact dermatitis (ACD).

Objective: Aim of the study was to verify the usefulness, to check the reliability in clinical practice and to evaluate the economic costs of AS previously built up.

Methods: A total of 281 patients with suspicious ACD underwent patch test with the standard series (SS) and with one or more AS (51 among 71 built up).

Results: A total of 170 patients (60.5%) showed positive reactions to SS; 116 (41.3%) to AS. Among 582 nonstandard allergens used, 113 (19.4%) elicited 1 or more positive reactions: out of 10,916 patch tests carried out, 260 (2.4%) positive reactions were observed. The correlation between SS and AS indicated that 8.2% patients resulted SS-/AS+, 27.7% SS+/AS-, 32.7% SS+/AS+, 31.3% SS-/AS-. The most frequently used AS showed the following percentages of patients with 1 or more positive reactions: clothes 41.4%, building industry 51.8%, hairdressers 77.3%, textile industry 42.1%, shoes 36.8%. Positive reactions to the most frequently used nonstandard allergens resulted: propylene glycol 0.4%, cobalt chloride 12.6%, phenylmercuric nitrate 2.2%, p-aminophenol 4.5%. The approximate economic cost of patch testing with AS has been evaluated in 1.3 euro per single patch test.

Conclusion: The cost of patch testing AS is not irrelevant, but it can be compensated by the advantages deriving from the increase of data concerning ACD etiology. A reduction in the number of allergens included in single AS should be performed. Cobalt chloride, taking into account the high percentage of positive reactions observed and its presence in a large number of AS, could be (re)introduced in the standard series.