A food allergy is defined as an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food.
New guidelines from an expert panel sponsored by the National Institute of Allergy and Infectious Diseases (NIAID) aim to standardise the diagnosis and management of food allergy across clinical care settings.[1] The recommendations also addressed the use of multiple types of tests for reaching a diagnosis for IgE-mediated food allergy:
Food allergens are defined as those specific components of food or ingredients within food (typically proteins, but sometimes also chemical haptens) that are recognised by allergen-specific immune cells and elicit specific immunologic reactions, resulting in characteristic symptoms. Some allergens (most often from fruits and vegetables) cause allergic reactions primarily if eaten when raw. However, most food allergens can still cause reactions even after they have been cooked or have undergone digestion in the stomach and intestines. A phenomenon called cross-reactivity may occur when an antibody reacts not only with the original allergen, but also with a similar allergen. In FA, cross-reactivity occurs when a food allergen shares structural or sequence similarity with a different food allergen or aeroallergen, which may then trigger an adverse reaction similar to that triggered by the original food allergen. Cross-reactivity is common, for example, among different shellfish and different tree nuts.
Foods or food components that elicit reproducible adverse reactions but do not have established or likely immunologic mechanisms are not considered food allergens. Instead, these non-immunologic adverse reactions are termed food intolerances. For example, an individual may be allergic to cow’s milk (henceforth referred to as milk) due to an immunologic response to milk protein, or alternatively, that individual may be intolerant to milk due to an inability to digest the sugar lactose. In the former situation, milk protein is considered an allergen because it triggers an adverse immunologic reaction. Inability to digest lactose leads to excess fluid production in the gastrointestinal (GI) tract, resulting in abdominal pain and diarrhea.
The author’s state:
“The exercise of diagnosing a food allergy is not just doing a skin test, or not just doing a blood test, or not even just having a report of a food allergy,” Sampson said. “It takes a combination of a good medical history as well as some laboratory tests and in some cases an oral food challenge in order to make the appropriate diagnosis.”
The recommendations also addressed the use of multiple types of tests for reaching a diagnosis for IgE-mediated food allergy:
- A skin prick test should be used to identify foods that may be provoking an allergic reaction, but it cannot stand alone for diagnosis. Intradermal testing and routine use of measuring total serum IgE should not be used to make a diagnosis.
- Allergen-specific IgE tests should be used to identify foods that could potentially provoke allergic reactions, but are not diagnostic of food allergy alone.
- An atopy patch test should not be used in routine evaluation of noncontact food allergy.
- A combination of skin prick tests, allergen-specific IgE tests, and atopy patch tests should not be used for routine diagnosis.
- Several nonstandardised procedures should not be used for diagnosis, including the allergen-specific IgG4 test used by some clinicians.
- Oral food challenges should be used for diagnosing food allergy. A double-blind, placebo-controlled food challenge is the gold standard, although a single-blind or open food challenge may be considered diagnostic in two cases: if either of these challenges elicits no symptoms, then food allergy can be ruled out. But when either type of food challenge elicits symptoms consistent with medical history and are supported by lab tests, then a diagnosis of food allergy is supported.
Comment
Nutritional Therapists have long championed the use of food challenges in relation to food allergy, but they also use other strategies, including the controversial IgG tests and others.
Here is a conservative body recommending that the gold standard if food challenge – a technique we are all familiar with – however, we also know that many people have an improvement in their health on the elimination of a food group from their diet despite lack of convincing lab work but plenty of clinical feedback. The most common food agent that attracts most confusion are wheat/gluten. The no man’s land between gluten intolerance and full blown coeliac falls outside of the food allergy diagnosis but remains one of the most common of all food reactors.[2]
References
[1] Boyce J, et al “Guidelines for the diagnosis and management of food allergy in the U.S.: summary of the NIAID-sponsored expert panel report” J Allergy Clin Immunol 2010; 126: 1105-1118. View Full Paper
[2] Verdu EF, Armstrong D, Murray JA. Between celiac disease and irritable bowel syndrome: the “no man’s land” of gluten sensitivity. Am J Gastroenterol. 2009 Jun;104(6):1587-94. Review. View Abstract
