Food Challenges

There are many tools that can help suggest the presence of food allergies, but, in the end, the most reliable procedure to confirm or exclude a diagnosis of food allergy remains the oral challenge.  But how should allergists perform them?  In this month’s issue of JACI, Drs. Ballmer-Weber and Beyer provide their insights on how to effectively conduct a food challenge (J Allergy Clin Immunol 2018; 141(1): 69-71).   The majority of children with food allergies require such challenges to diagnose their condition, especially younger children with eczema who have skin prick or blood tests suggesting that allergic sensitization may be a trigger for eczema flares, or in whom a food allergy may no longer be present.  However, not all patients should have challenges.  The risks of a severe, life-threatening anaphylactic reaction have to be balanced with the benefits of more definitively establishing a diagnosis.  In addition, the risks of an oral challenge may be too high in those who are pregnant, have unstable asthma, or take medications that would interfere with the treatment of challenge-induced allergic reactions, such as Beta-blockers.  The presence of other conditions, like hives, uncontrolled eczema, allergic rhinitis, mast cell disorders, or acute infection may make interpretation of results difficult and therefore influence an allergist’s decision to pursue an oral challenge.  Regardless, a very careful examination is necessary beforehand.  Once the decision is made, increasing doses of a particular food are given, usually every 30 minutes, but there is considerable flexibility in the amount of food, number of steps, and the time in between each step.  Throughout the challenge, patients have to be monitored.  If there are any objective signs of food allergy, the challenge should be stopped and treatment started.  If the patient tolerates the challenge with no reaction, then the food should be taken at least three times per week to maintain tolerance.  Although it is the most accurate tool that the allergist has, false-positive results do occur, in as many as 1 out of 25 challenges.  False-negative results can also occur, especially if the food allergy tends to occur with an additional cofactor which was not accounted for in the challenge, like alcohol use, exercise, or viral infection.  In conclusion, oral challenges are a powerful tool to identify food allergies, but safety always comes first and results have to be placed in their right clinical contexts.

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