Comparing reliabilities of strip and conventional patch testing

Abstract

Background. The standardized protocol for performing the strip patch test has proven to be valid, but evidence on its reliability is still missing. Objective. To estimate the parallel-test reliability of the strip patch test as compared with the conventional patch test. Methods. In this multicentre, prospective, randomized, investigator-blinded reliability study, 132 subjects were enrolled. Simultaneous duplicate strip and conventional patch tests were performed with the Finn Chambers (R) on Scanpor (R) tape test system and the patch test preparations nickel sulfate 5% pet., potassium dichromate 0.5% pet., and lanolin alcohol 30% pet. Reliability was estimated by the use of Cohen's kappa coefficient. Results. Parallel-test reliability values of the three standard patch test preparations turned out to be acceptable, with slight advantages for the strip patch test. The differences in reliability were 9% (95% CI: -8% to 26%) for nickel sulfate and 23% (95% CI: -16% to 63%) for potassium dichromate, both favouring the strip patch test. Conclusions. The standardized strip patch test method for the detection of allergic contact sensitization in patients with suspected allergic contact dermatitis is reliable. Its application in routine clinical practice can be recommended, especially if the conventional patch test result is presumably false negative.