Repeated open application tests (ROAT) in patients allergic to colophony--evaluated visually and with bioengineering techniques.

It is desirable to further evaluate the clinical relevance of a positive patch test. The repeated open application test (ROAT) has been suggested as such a supplementary method. To compare the results of patch testing with the outcome of ROATs, 13 colophony-sensitive subjects and 9 controls were patch-tested with colophony in a serial dilution test. Five microliters, of three concentrations of a colophony solution and the vehicle were then applied to small test areas on the lower arm, once daily for 2 weeks. Prior to each application, all test sites were examined visually and with bioengineering techniques. In the ROATs, 10/13 colophony-sensitive subjects--but no controls--reacted to a 20% colophony solution, 4 also 1%. A correlation was found between the threshold concentration at patch testing and the outcome of ROATs. There was great variation in the reactivity in the ROATs. Objective measures for evaluating the ROAT reactions gave no further information than visual assessment.