Detection of contact allergy: using more extensive test series increases the diagnostic efficacy of patch tests.

BACKGROUND Contact allergy is the most frequent type of allergy, affecting 26-40% of all adults and 21-36% children. The gold standard in the diagnosis of contact allergy is patch test. OBJECTIVE To study the influence of the range and composition of patch test series on the efficacy of the diagnostic procedure. MATERIAL AND METHODS Retrospective analysis of the frequency of positive reactions among patients diagnosed with patch tests at our Department during 2 periods: From December 2003 to March 2005, patients were tested with a series of 9 substances plus white petrolatum as the negative control. From April 2005 to July 2008, the series was expanded to 21 substances, while petrolatum was removed. RESULTS In the analyzed period, 1379 patients were tested with 9 substances plus petrolatum (group referred to as "G9") and 682 patients with 21 substances ("G21"). In G9, at least one positive reaction was observed in 343 (24.9%, 95% CI: 22.6-27.2%) patients, as compared to 376 (55.1%; 95% CI: 51.4-58.7%) in G21 (p < 0.0001). The increase in the number of tested substances from 9 to 21 led to significant increase in the mean number of positive reactions per one patient (0.34 in G9 versus 0.90 in G21; p < 0.0001). We have not observed any positive reaction to white petrolatum. CONCLUSIONS Patch testing with more extensive test series increases the chance for the detection of patient's sensitizations. As we have not observed any positive reaction to white petrolatum, using the vehicle as negative control does not seem to offer any advantage.