A double-blind study of symptom provocation to determine food sensitivity.
BACKGROUND: Some claim that food sensitivities can best be identified by intradermal injection of extracts of the suspected allergens to reproduce the associated symptoms. A different dose of an offending allergen is thought to "neutralize" the reaction. METHODS: To assess the validity of symptom provocation, we performed a double-blind study that was carried out in the offices of seven physicians who were proponents of this technique and experienced in its use. Eighteen patients were tested in 20 sessions (two patients were tested twice) by the same technician, using the same extracts (at the same dilutions with the same saline diluent) as those previously thought to provoke symptoms during unblinded testing. At each session three injections of extract and nine of diluent were given in random sequence. The symptoms evaluated included nasal stuffiness, dry mouth, nausea, fatigue, headache, and feelings of disorientation or depression. No patient had a history of asthma or anaphylaxis. RESULTS: The responses of the patients to the active and control injections were indistinguishable, as was the incidence of positive responses: 27 percent of the active injections (16 of 60) were judged by the patients to be the active substance, as were 24 percent of the control injections (44 of 180). Neutralizing doses given by some of the physicians to treat the symptoms after a response were equally efficacious whether the injection was of the suspected allergen or saline. The rate of judging injections as active remained relatively constant within the experimental sessions, with no major change in the response rate due to neutralization or habituation. CONCLUSIONS: When the provocation of symptoms to identify food sensitivities is evaluated under double-blind conditions, this type of testing, as well as the treatments based on "neutralizing" such reactions, appears to lack scientific validity. The frequency of positive responses to the injected extracts appears to be the result of suggestion and chance.