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

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

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.

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).

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.

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.