Adverse reactions to foods or food allergies are on the rise among children around the world. In Singapore, 5% of children have a diagnosed food allergy1.
The top 8 allergenic food groups which account for the majority of food reactions include cow’s milk (dairy), soy, egg, wheat, peanuts, treenuts, fish, and shellfish2,3.
When do food allergies present?
Most food reactions are immediate-type (or IgE-mediated) food allergies and present soon within minutes to a couple of hours after consumption of the food.
Not all food reactions will occur after the first consumption of the new food.
Most often, it will require a few repeated intakes before symptoms of allergies present. This is because the initial few exposures of the food to a naïve immune system in the child then cause the development of allergic antibodies which are then able to initiate the allergic response during the subsequent exposures.
What symptoms occur during a food reaction?
The most common allergic manifestations involve the skin (redness, itchy rashes, hives, and facial swelling), followed by gastrointestinal symptoms (vomiting, abdominal pains, and diarrhea) and respiratory symptoms (noisy breathing or wheezing).
Symptoms can be mild to severe and life-threatening (anaphylaxis). Hence, it is important to recognize the symptoms of an allergic reaction and seek treatment early.
How is a food allergy diagnosed?
The diagnostic workup for a food allergy includes a detailed patient history. This would include a detailed prior food history, a thorough investigation of ingredients consumed, and details of the reaction and timing with regard to exposure.
A detailed food diary kept by parents is often helpful in the workup of a possible food reaction. Any pictures available of visible symptoms such as rashes or swelling will also be useful in the evaluation.
The next step of the workup will include diagnostic investigations guided by the initial history taken. The preference is often for skin prick tests in children which are as accurate as blood-specific IgE antibody testing in allergy diagnosis4.
Allergy diagnostic tests should be performed 4-6 weeks after an allergic reaction to reduce the chances of a false negative result being obtained.
The skin prick test is usually preferred because it is a safe, painless, and quick procedure with results received within 20 minutes of the test. This allows for a proper full evaluation to be conducted by the allergist within the same visit.
What is an oral food challenge and when is it performed?
The gold standard diagnostic test for the evaluation of a food allergy is the oral food challenge. Food challenges are commonly performed for the initial diagnosis of a food allergy (due to the small possibility of false positive allergy tests) and to determine if a child is outgrowing his/ her food allergy. Food challenges are not performed if there is already a high likelihood of an allergic reaction as predicted by the food reaction history or allergy skin or blood tests.
Where the likelihood of a true allergic reaction is doubtful, food challenges are helpful in avoiding unnecessary food restrictions and are performed in a safe and step-wise manner under close supervision and monitoring in an allergist’s office.
References:
- National Institute for Health and Clinical Excellence. Food allergy in children and young people: draft scope for consultation. 2010.
- Burks AW, James JM, Hiegel A, et al. Atopic dermatitis and food hypersensitivity reactions. J Pediatr 1998;132:132–6. 6.
- Niggemann B, Sielaff B, Beyer K, et al. Outcome of double-blind, placebo-controlled food challenge tests in 107 children with atopic dermatitis. Clin Exp Allergy 1999;29:91–6.
- Hill DJ, Heine RG, Hosking CS. The diagnostic value of skin prick testing in children with food allergy. Pediatr Allergy Immunol 2004;15:435–41.
Written by Dr Mohana Rajakulendran on 11 October 2022
