Skin Prick Testing
Tree nut SPT will include both fresh tree nuts and commercial extracts
almond, cashew pecan (Greer), brazil nut, pistachio, walnut (ALK USA)
and hazelnut and macadamia (Immunotek)]. Peanut SPT will be via
commercial extract only (Greer). Any participant reacting to the
multi-nut OFC or on home introduction of an individual tree nut will
undergo SPT to tree nuts. At 18 months of age follow up peanut and tree
nut SPT will be performed regardless of ingestion or allergy history to
capture sensitized tolerant participants.
Allergens will be applied to the child’s back and standard single lancet
technique will be used with a Quintip device. Wheal size will be
calculated as the average of the length and width of the wheal after 15
minutes. A positive SPT will be defined as a wheal diameter at least 3
mm greater than that produced by the negative control solution at 15
minutes. For allergens tested with extract and fresh nuts, a mean
wheal diameter ≥3 mm for either method will be considered positive.
Individual Nut Oral Food Challenge s
Participants sensitized to peanut or any tree nut will undergo
individual nut OFC using a modified version of the Australasian Society
of Clinical Immunology and Allergy (ASCIA) Peanut or Tree Nut Challenge
Protocols [22]. The top dose has been reduced from 2 teaspoons to
one teaspoon for the TreEAT trial due to the younger age of
participants. The individual peanut or tree nut OFC will consist of 6
increasing doses at 20minute intervals (Smear, 1/16tsp, 1/8tsp, ¼ tsp,
1/2tsp and 1 tsp).
A positive multi nut or individual nut food challenge will be defined
based on modified PRACTALL criteria [23] and in summary will consist
of any one of the following: ≥3 concurrent non-contact urticarial
wheals, facial angioedema, vomiting and /or anaphylaxis (respiratory or
cardiovascular symptoms) within 1 hour of the last dose.