The validity of electrodermal screening, a method used by some alternative practitioners to detect allergies, has been challenged by a study published in the British Medical Journal in 2003.
Electrodermal screening is based on the principle that slight changes in the electrical impedance of a person's skin occurs when an allergen is placed on an electrical circuit.
The testing procedure works like this: the patient holds an electrode that is connected by circuit to a probe held by the examiner.
The examiner places an allergen in a holder on the circuit and then touches the probe to an acupuncture point on the patient's skin. The greater the sensitivity of the patient to the allergen, the higher the reading on the galvanometer. The test is usually repeated using an array of foods and environmental substances.
The researchers, led by Dr. George Lewith from the University of Southampton, compared electrodermal testing to skin probe testing, a conventional method for detecting allergies. Thirty participants were enrolled in the study, including fifteen who had tested positive for allergy to either the house dust mite or cat dander using the skin prick test and fifteen who had tested negative.
Three examiners independently tested each participant in order to address concerns that test results can vary greatly among different examiners. Critics also claim that examiners can unconsciously apply greater pressure over certain acupuncture points, based on their expectations.
The study found that the examiners could not correctly identify the participants with predetermined allergies. Furthermore, no single operator was more reliable at detecting allergies than another, and no participants were consistently given a correct diagnosis by the three examiners.
This study suggests that electrodermal testing is not effective in diagnosing allergies to cat dander and the house dust mite. Due to the small size of the study, larger, well-designed studies are needed to further assess the effectiveness of electrodermal testing. It would be interesting to see the effectiveness of this method for detecting food allergies and for selecting homeopathic remedies, which are other uses of this method.
Lewith GT, Kenyon JN, Broomfield J, Prescott P, Goddard J, Holgate ST. Is electrodermal testing as effective as skin prick tests for diagnosing allergies? A double blind, randomised block design study. BMJ 2001;322:131-4.