Sicherer, Morrow and Sampson evaluated retrospectively the quantity of food that had been needed to elicit reactions during challenge testing in 196 children with atopic eczema and food allergies 1. The initial dose of the food was 0.4 to 0.5 g and the dose was gradually increased to 2.5 g, provided that the child remained symptom free. One verum and one placebo challenge were carried out in one day. The percentage of children reacting at the first dose was as follows: milk 55 %, egg 49 %, wheat 25 %, peanut 26 % and fish 17 %. Some of the milk and egg challenges were positive at a first dose of 100 mg. No significant negative correlation was noted between the symptom eliciting dose and skin prick test wheal size (-0.22 - +0.25 for particular allergens) or between the dose and the RAST result (-0.4 - 0.03). The study was carried out at a tertiary hospital (Mt. Sinai Hospital, NY) which treats a large number of children with severe food allergies. Based on their food-allergic population, the researchers recommend that lower doses (≤ 100 mg) should be investigated for their appropriateness in initiating food challenges. The dose causing a reaction cannot be predicted by the size of a skin prick wheal or RAST result.
Bock and Atkins reported on 1,014 food challenges carried out over 16 years in 480 children 2. Thirty-nine per cent of the challenges were positive. The age of the children ranged from 3 months to 19 years. The doses eliciting a positive reaction varied from 20 mg to 10 g of dried food. The most positive reactions (n) were caused by egg (62), peanut (59), milk (57), other nuts (25), soya (15), fish (8) and wheat (6). Twelve patients with a negative challenge test became symptomatic during a later, open challenge. The symptoms were likely to be related to the direct skin or mucous membrane contact of an open challenge and/or to the higher food dose.
Hourihane et al. evaluated with a double-blind challenge test the sensitivity of adult subjects with severe peanut allergy to very low doses of peanut protein 3. The challenge was carried out by administering peanut flour with a protein content of 46 %. The following doses were used: 10, 20, 50, 100, 250 and 500 mg (1, 2, 5, 10, 20 and 50 mg of protein), provided that the patient remained symptom free. The lowest dose that elicited a positive reaction was 2 mg of protein. Even smaller doses (100 mg) provoked subjective symptoms in some subjects.
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