The importance of context information in the diagnostic rating of digital images of patch test reactions.
BACKGROUND
Patch test (PT) guidelines recommend classifying PT reactions based on morphological criteria only, i.e. irrespective of context information such as substance, concentration and vehicle.


OBJECTIVE
To analyse reclassification of PT reactions after revelation of context information subsequent to an initial blinded reading.


METHODS
One hundred and twenty-two participants (experienced dermatologists and researchers) rated 20 digital images of different PT reactions twice, first blinded, then unblinded regarding substance, concentration and vehicle. Agreement between both ratings was quantified with Cohen's kappa, and systematic differences statistically examined with tests for marginal homogeneity.


RESULTS
Mostly, ratings remained stable, e.g. in > 90% of cases of images showing typical strong or extreme positive PT reactions. Reclassification was comparatively often observed in images depicting irritant reactions. Conversely, 16 of 122 participants re-rated doubtful reactions to thiuram mix and dichromate, respectively, as 'allergic' (weak or strong positive) after knowing the substance.


CONCLUSIONS
The considerable proportion of participants who choose an 'allergic' rating, despite a morphological presentation definitely not justifying this, points to a conceptual problem of the PT reading scale: the mixing up of morphological classification and interpretation. We therefore suggest amending the scale. Moreover, standardization of PT reading can be improved by continual PT training sessions.
Department of Dermatology, University of Witten/Herdecke and Klinikum Dortmund gGmbH, Dortmund, Germany.
W
W
Uter
P J
PJ
Frosch
D
D
Becker
A
A
Schnuch
A
A
Pfahlberg
O
O
Gefeller
D000485:Allergens; D017449:Dermatitis, Allergic Contact / Q000175:diagnosis*; D003880:Dermatology; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000592:standards*; D015588:Observer Variation; D010328:Patch Tests / Q000592:standards*; D015203:Reproducibility of Results
D000485:Allergens