For a double-blind placebo-controlled food challenge (DBPCFC), the patient is exposed to gradually increasing doses of the suspected food, hidden in a matrix. The DBPCFC can be performed in a 1- or a 2-day approach. During a 1-day approach, placebo doses containing an identical matrix are randomly interspersed. During a 2-day approach, one day consists of verum doses, and one day of placebo. The order of the verum and placebo days are random. The DBPCFC is performed in a hospital setting, with a trained nurse and full emergency medication readily available.
The challenge is discontinued when objective symptoms occur, or when consistent subjective symptoms occur on at least 3 subsequent doses. The lowest dose that induces an allergic reaction is the so-called eliciting dose (ED). The symptoms are treated with appropriate medication. Reactions such as oropharyngeal symptoms, nausea and abdominal pain are considered subjective symptoms. Objective symptoms indicative of an allergic reaction include urticaria, facial swelling, rhinoconjunctivitis, vomiting, diarrhea, dyspnea, bronchoconstriction, and tachycardia. Symptoms are graded according a scale adapted from the Mueller score for insect venom allergy ((Mueller HL. Diagnosis and Treatment of Insect Sensitivity. J Asthma Res 1966;3:331–3. doi:10.3109/02770906609106941)).
This score ranges symptoms as follows:
Müller 0: oropharyngeal symptoms
Müller 1: symptoms of skin and mucous membranes (urticaria, angiooedema, flush, rhinoconjunctivitis, pruritis)
Müller 2: gastrointestinal symptoms (diarrhea, vomiting, nausea, abdominal pain)
Müller 3: respiratory symptoms (larynx oedema, asthma, hoarseness)
Müller 4: cardiovascular symptoms (drop in blood pressure, shock)