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.

Food allergy: Update on prevention and tolerance

The rate of food allergies in the United States keeps on rising, but nobody really knows the exact reasons why.  In this month’s issue of the Journal of Allergy and Clinical Immunology, Du Toit and colleagues review the literature and focus on the ‘dual allergen’ hypothesis (J Allergy Clin Immunol 2018; 141(1): 30-40).  Briefly, they explain that allergic sensitization may occur when there is low-level skin exposure to food allergens, while tolerance is more likely to develop in children to have early exposures to food proteins.  The data are mounting from both animal and human observational studies as well as randomized control studies.  The most notable has been the LEAP study, which showed that infants aged 4 to 11 months who consumed peanut products at least three times per week until age 60 months were far less likely to develop peanut allergies than infants who had complete avoidance.  Only 3.2% in the peanut-eating group developed peanut allergy, compared to 17.2% in the complete avoidance group.  The follow-up study, LEAP-On, demonstrated persistence of this tolerance for at least 12 months, even with strict avoidance in non-peanut allergic children.  Similarly, the EAT study suggested that lower rates of food allergies with early introduction of allergenic foods in breastfed infants, although conclusions were less clear-cut than in the LEAP study.  The results of other studies have been more variable.  Regardless, the LEAP and EAT studies show that early introduction of allergenic foods into infant diet is achievable and safe, and does not affect breastfeeding rates as well as later nutrition and growth.  However, there are a lot of challenges.  Ensuring adherence to dietary recommendations, determining the dosages of food proteins, and powering studies sufficiently to show meaningful differences are challenges that researchers and clinicians face.  This has led to the National Institutes of Health’s recommendation for early peanut introduction to prevent peanut allergy.  Other countries have also recommended inclusion of potential common food allergens in complementary feeding regimens at around 6 months.  With more research, it is possible that we may find more effective ways to help prevent food allergies.