Objective non-invasive assessment of patch tests with the laser Doppler perfusion scanning technique

The laser Doppler perfusion scanning technique is an objective, non-invasive assessment method that may be used to assess patch tests. The purpose of this paper is to focus on its clinical use in individuals with light skin, tested with non-pigmented test materials. A laser Doppler perfusion imager PIM 1.0 (LDPI) is used to study different set-ups of the instrument that may affect readings. These set-ups are studied through simulated light-absorbing patch tests. The results have served as a base for clinical experiments comparing visual and LDPI assessments of normal skin, irritant patch-test reactions, and more than 25,000 allergic patch-test assessments of reactions of different intensities and control patches. This paper reviews the clinical experiments to suggest a set-up of the LDPI for patch-test readings. Such a set-up makes it possible to compare intra- and inter-individual test results and to obtain meaningful assessment values among users. Some subject-related factors that may affect reading results are studied, and the effect of non-subject related factors on readings are considered. Use of the technique is illustrated by images of perfusion and a perfusion profile of a patch-test reaction followed over time.