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Food allergy (FA) is a common condition in early childhood, affecting up to 10% of children under 5 years. It is defined as an adverse immunologic reaction to a food protein. Many FA are IgE-mediated immediate hypersensitivity reactions, while immunologic mechanisms other than IgE also occur. These are referred to as non IgE-mediated reactions. Food intolerance does not have an immunologic mechanism.
A useful overview can be found in the recently published article: Food allergy: A review and update on epidemiology, pathogenesis, diagnosis, prevention, and management Scott H Schierer, MD and Hugh Sampson, MD. J Allergy Clin Immunol, Jan 2018. See http://www.jacionline.org/article/S0091-6749(17)31794-3/fulltext#pageBody to access the full article
Guidelines on the diagnosis and management of food allergy are available as follows:
- "IgE-mediated food allergy - diagnosis and management in New Zealand children" (Sinclair et al, NZMJ 2013) provides an overview of clinical guidelines for New Zealand.
- The Australasian Society of Clinical Immunology and
Allergy (ASCIA) has published an evidence-based, 'quick
reference guide' to assist health professionals in the management
of patients with IgE and non-IgE mediated food allergy http://www.allergy.org.au/images/stories/pospapers/ASCIA_HP_Clinical_Update_Food_Allergy_2016_HP_version_UPDATED.pdf
This complements ASCIAs food allergy e-training for health professionals, which is recommended by the Allergy Clinical Network. There is no charge for this and other ASCIA e-training modules. See Training and Resources for more information and links to these courses.
- The Irish Food Allergy Network has provided a useful summary of food allergy: http://ifan.ie/food-allergy-in-summary/summary/
Diagnosis is based on clinical history, with the history of an immediate allergic reaction critical in the interpretation of skin-prick test (SPT) or serum specific IgE (ssIgE, also referred to as RAST or EAST).
The Allergy CN recommends an approach to diagnosis including testing as follows:
- Allergy focussed history
Most food allergic reactions are due to a small number of foods, with milk, egg, peanut, nut, sesame, fish, shellfish, kiwifruit, wheat and soy accounting for the large majority of reactions.
Most food allergic reactions come on quickly after eating a new food - 75% of milk and peanut reactions occur on first known ingestion. Onset of IgE mediated reactions is often within minutes and almost always within a couple of hours. Food allergic reactions tend to completely resolve within hours.
Signs and symptoms
IgE mediated reactions can include a variety of signs and symptoms, and no one feature is always present. Common signs and symptoms are listed on the ASCIA action plans https://www.allergy.org.au/health-professionals/ascia-plans-action- and-treatment
- What to test
Allergy skin prick tests (SPT) and specific IgE (ssIgE, previously also referred to as RAST or EAST) are not screening tests. They are easiest interpreted when there is a clinical history of food allergy. Where there is a positive test but no history of food allergy, the test may indicate sensitisation rather than true allergy, and may lead to inappropriate and unnecessary food exclusion.
Sometimes anticipatory testing may be useful - e.g. many paediatricians and allergy specialists suggest testing tree nuts if a child has had a reaction to peanut, or if a child has multiple food allergies on history then testing a broader range may be needed. These decisions should be made by the specialist who sees the child in discussion with the family
- Conditions where food allergy testing is not
If there is no history of an IgE mediated food allergic reaction (see www.allergy.org.au ) then food allergy testing is not indicated. The down side to food allergy testing is that it may detect sensitisation rather than clinical allergy, and lead to inappropriate and unnecessary food avoidance. This could potentially result in loss of previous tolerance, or could increase the long term chance of developing clinical food allergy.
This applies to children with eczema where there is no history of immediate food allergic reaction. Children with eczema have an increased chance of also having food allergy, but food allergy does not cause eczema, and there is no good data that food avoidance is useful in the management of eczema. Resources for eczema management can be found at /for-health-professionals/new-zealand-child-and-youth-clinical-networks/child-and-youth-eczema-clinical-network/
- Conditions where dietitian referral is
Removal of dairy +/or wheat from a child's diet can lead to a restricted diet if appropriate food substitutes are not included. This can impact micronutrient intake such as calcium and reduce overall calorie intake which can result in growth issues.
Othe rresources for health professionals include:
Signs and symptoms of an IgE-mediated allergic reaction:
*Features of anaphylaxis, defined as a severe allergic reaction with involvement of cardiovascular and/or respiratory systems.
Specialist paediatric referral and dietetic support is recommended for children with food allergy with:
- Definite or possible anaphylaxis.
- Allergy to cow's milk or multiple food allergies, where expert advice is needed.
- Where there is uncertainty about the diagnosis or interpretation of results.
- Food sensitisation on ssIgE / SPT, where supervised challenge may be necessary to clarify whether there is clinical allergy.
- Allergy to foods such as peanut and nut where the risk of severe allergic reactions is higher.
- Children with asthma and FA, with asthma a risk factor for severe food allergic reaction on accidental exposure.
- Children whose FA persists past 5 years of age.
Allergen avoidance, risk management (particularly in relation to the potential for anaphylaxis), dietetic support, and follow-up are the main features of the management of food allergy. Eventual referral for specialist supervised food challenge may be necessary. Patient education in all aspects is important. Patients should be provided with an Action Plan - Allergy or Anaphylaxis - signed by their doctor. These are available from the ASCIA website on:http://www.allergy.org.au/health-professionals/anaphylaxis-resources. The Paediatric Allergy Clinical Network also has more information on the management of anaphylaxis.
Dietetic support is recommended for children with allergy to cow's milk. Information on the calcium needs of children with cow's milk allergy is available here, or parents/families can view the information on www.kidshealth.org.nz
Clinical Update for Dietitians: ASCIA has
published a Clinical Update to complement the ASCIA food allergy
e-training for dietitians. The main purpose of this document is to
provide an evidence-based, 'quick reference guide' to assist
dietitians in the management of patients with IgE and non-IgE
mediated food allergy. The Clinical Update for Dietitians is
Document last reviewed: November 2018
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