History gathering, as discussed earlier, should concentrate on the most likely foods and symptoms. Clearly some patients will not be suitable for a food challenge. Some patients will not be prepared to have what may be strongly held beliefs investigated, and the history should include some assessment of the suitability of the patient for the procedure. Other pieces of additional information essential for the design of the challenge include the timing between the ingestion of the food and the onset of symptoms, the amount of food necessary to produce symptoms, and finally any adjuvant factors such as exercise that are necessary for the onset of symptoms. Nearly all the foodstuffs positively incriminated cause symptoms within hours of ingestion (except protein-sensitive enteropathies). Some patients may give very specific symptoms that have measurable parameters, useful as outcome measures of the DBPCFC. Respiratory symptoms can be monitored using pulmonary function tests and bronchial provocation challenges. Peak expiratory flow rate (PEFR) and the forced expiratory volume in one second (FEV1) are the most reproducible measures affected during bronchoconstriction (narrowing of the airways). Specific bronchial provocation challenges can be useful in the diagnosis of food allergies. These have been employed particularly in the confirmation of occupational or industrial asthma. Specific bronchial challenges, using aerosol preparations of the implicated allergens, can be used to demonstrate resultant bronchoconstriction.22
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