Is electrodermal testing as effective as skin prick tests for diagnosing allergies? A double blind, randomised block design study

Objective To evaluate whether electrodermal testing for environmental aller gies can distinguish between volunteers who had previously reacted positive ly on skin prick tests for allergy to house dust mite or eat dander and vol unteers who had reacted negatively to both allergens. Design Double blind, randomised block design. Setting A general practice in southern England. Participants 15 volunteers who had a positive result and 15 volunteers who had a negative result on a previous skin prick test for allergy to house du st mite or cat dander. Intervention Each participant was tested with 6 items by each of 3 operator of the Vegatest electrodermal testing device in 3 separate sessions (a tot al of 54 tests per participant). For each participant the 54 items comprise d 18 samples each of house dust mite, cat dander, and distilled water, thou gh thee were randomly allocated among the operators in each session. A rese arch nurse sat with the participant and operator in all sessions to ensure blinding and adherence to the protocol and to record the outcome of each te st. Outcome The presence or absence of an allergy according to the standard pro tocol for electrodermal testing. Results All the non-atopic participants completed all 3 testing sessions (8 10 individual tests); 774 (95.5%) of the individual tests conducted on the atopic participants complied wit the testing protocol. The results of the e lectrodermal tests did not correlate with those of the skin prick tests. El ectrodermal testing could not distinguish between atopic and non-atopic par ticipants. No operator of the Vegatest device was better than any other,and no single participant's atopic status was consistently correctly diagnosed . Conclusion electrodermal testing cannot be used to diagnose environmental a llergies.