Intradermal testing for food and chemical sensitivities: A double-blind controlled study

Background: Confirming adverse reactions to foods and chemicals is fundamen tal in providing a basis for diagnosis and treatment of patients with repor ted environmental sensitivities. Provocation-neutralization testing is wide ly used in this respect but has not been thoroughly evaluated, therefore re maining a controversial and unproven technique. Objective: This study investigated the validity of intradermal testing for evaluation of reported adverse reactions to a variety of incidents within t he patient population at the Nova Scotia Environmental Health Centre, Methods: A total of 132 people who were referred to the Nova Scotia Environ mental Health Centre, a dedicated government-funded research and treatment facility for suspected environmental sensitivities, were tested by the tech nique of provocation-neutralization by the guidelines set out by the Americ an Academy of Environmental Medicine. A panel of 13 foods, 9 chemicals, and 4 placebos (normal saline solution) was evaluated in a double-blind, rando mized study. Symptoms and skin reactions were recorded, and response rates were determined for all substances, including saline solution injections. Results: Seventy percent of the patients reported symptoms to 1 or more of the 4 saline solution injections. In comparison, 15% of patients experience d a skin reaction (wheal) to 1 or more injections of saline solution. Only 5% of individuals experienced a wheal to more than 1 saline solution inject ion, although 40% of the patients reported symptoms to more than 1 saline i njection. Patients who experienced 1 or more reactions (wheal or symptoms) to saline solution were more reactive to injected allergens, on average rea cting to 67% of active substances. Patients who experienced no reaction to the saline solution did experience a reaction to 48% of injected substances on average. Reaction by symptoms to foods, chemicals, and normal saline so lution showed a random pattern, although wheal reactions showed a distinct pattern. Subsequent observations hare indicated that experiencing no reacti on to previous saline solution injections does not accurately predict respo nse to saline solution in later testing. Some individuals who did not exper ience a reaction to saline solution in an initial screening later experienc ed a reaction to saline solution during further testing. Conclusions: Provocation of symptoms in usual testing conditions is not a u seful tool for discriminating between reactions to saline solution and reac tions to specific chemicals or foods. Skin response alone may be a more rel iable indicator and will require cross-validation with other tests, such as oral and inhalation challenges and comparison with a control population. H eightened sensitivity and chaotic responses may be a feature of chemical se nsitivity. Meanwhile, the results of provocation-neutralization testing, us ing symptoms alone as an indicator of neutralization, should not be used as a basis for clinical intervention.