Comparison of reactivity to allergens using the TRUE Test and IQ chamber system

The reproducibility of the patch test is of great importance to its diagnostic utility. The objective of this study was to quantitatively and qualitatively compare the reproducibility of patch test reactions between the manufacturer-loaded TRUE Test (TT) panel and the investigator-loaded IQ Chamber (IQC) system using the European Standard Series (ESS) (Chemotechnique Diagnostics, Malmö, Sweden). Consecutive patients were simultaneously patch tested with 21 allergens using the TT and IQC system. The concordance and discordance of the 2 methods were analysed. Testing was performed in 207 patients (85 men and 122 women) who yielded 317 positive reactions, 188 with the IQ system and 129 with the TT. A total of 204 tests were positive with both methods, showing a positive concordance rate of 64.4%, with IQC producing more positive results. A high concordance rate of positive results was achieved for Cl+ Me- isothiazolinone (81.5%), nickel sulfate (79%), formaldehyde (76.9%), and paraphenylenediamine (PPD) (72.7%); a moderate concordance was noted for quaternium 15 (66.7%), potassium dichromate (64.3%), and fragrance mix (58.1%); and a low concordance was noted for cobalt chloride (27.6%) and Balsam of Peru (18.2%). The IQC and the TT are similar in finding allergy to allergens with high concordance. The IQC system has an advantage in detecting clinically relevant reactions to allergens that have a moderate and a low concordance.