FOOD ALLERGY: WHEN ARE SKIN PRICK TESTS AND EPIPENS INDICATED? Dr Imogen Norton Consultant Paediatrician Northampton General Hospital September 2012
OVERVIEW OF FOOD ALLERGY Definition Background Types of reaction Diagnosis Investigations Management Referral for food allergy Summary
WHAT IS FOOD ALLERGY? group of disorders characterised by an abnormal or exaggerated immunological response to specific food proteins that may be IgE or non- IgE mediated
BACKGROUND (1) Prevalence of food allergy is increasing and is currently about 6% in young children Food is the commonest cause of anaphylaxis in children During the 1990s, emergency admissions for anaphylaxis doubled
BACKGROUND (2) Food allergy in young children is usually caused by milk, egg, peanut, tree nuts, fish or shellfish Children with atopic diseases are more likely to have food allergies Can have a reaction on first exposure Most food allergies resolve in time
TYPES OF REACTION IgE mediated Exercise-induced Oral allergy syndrome Non-IgE mediated
IgE REACTIONS Occur when IgE antibodies are produced in response to allergen exposure Bind to mast cells causing degranulation and release of vasoactive amines and cytokines and synthesis of inflammatory mediators Permeability of small vessels increases, leading to swelling May develop cross-reactivity to other foods
EXERCISE-INDUCED Unknown mechanism Occurs if exercising after implicated foods Tends to occur in adolescents More common in females Often atopic
ORAL ALLERGY SYNDROME Itching, swelling or urticaria in/around mouth after ingesting food Usually tree fruits eg. peaches, plums, pears, cherries but also after vegetables Symptoms reduced by cooking fruits Local reaction only no systemic component
NON-IgE REACTIONS Inflammation mediated by lymphocytes and IgG Often occurs with histamine-containing foods eg. chocolate, tomatoes, strawberries
DIAGNOSIS OF FOOD ALLERGY History is key to management In particular: Suspected foods Time between ingestion and reaction Amount of food needed to cause reaction Frequency and reproducibility Signs and symptoms (skin, GI, resp)
SKIN PRICK TESTING Use of standardised allergen extracts Only indicated if food causing symptoms is known Positive predictive value 60% but rarely negative in true IgE mediated allergic reactions Positive skin prick test supports the diagnosis suspected from the history
SPT Common allergens tested Peanut Tree nuts Milk Egg Cod Shrimp
SPT Advantages Result in 15 mins Can plan management at same visit Disadvantages Can be tricky in young children Cannot be performed if antihistamines taken in previous 24-72 hours Difficult if widespread eczema Risk of anaphylactic reaction
RAST TESTING Blood tests to look at specific IgE Result graded 0-6 Can be used for wider range of foods Results can take 2-3 weeks Need caution in interpretation for children with eczema as high total IgE
FOOD CHALLENGE Gold standard for diagnosis of food allergy Can be used if history and investigations do not correlate Can be useful to reassure family that a particular food is safe Risk of anaphylaxis
MANAGEMENT OF FOOD ALLERGY Avoidance of allergen in conjunction with dietician Oral antihistamines for skin reactions Epipen Education of family, school and others Useful contacts eg. anaphylaxis campaign MMR
INDICATIONS FOR EPIPEN (1) Risk of fatal reaction higher in children with asthma requiring regular inhaled steroid Fatal reactions more common with milk and peanut
INDICATIONS FOR EPIPEN (2) Those at risk of anaphylaxis: Previous life-threatening reaction or airway compromise Severe or poorly controlled asthma (regular inhaled steroids) Strongly positive skin prick test Mild reaction with only trace exposure
EPIPEN CONSIDERATIONS (1) Appropriate dose Adult Epipen if >30kg (0.3mg adrenaline) Epipen Junior if <30kg (0.15mg adrenaline) When to use Airway compromise, collapse or if in doubt How to use Intramuscular injection into upper outer thigh through clothing
EPIPEN CONSIDERATIONS (2) Need two epipens prescribed one at home, one at nursery/school Epipens need to be in date Protect from heat and light Information leaflet Training of family, teachers etc. Regular retraining to maintain knowledge
WHO TO REFER FOR SPT Any child with allergic reaction soon after eating specific food Older child who may have grown out of food allergy No benefit in referring those with no obvious food trigger and mild reaction only Children with recurrent urticaria will not benefit from skin prick testing
SUMMARY Food allergy and anaphylaxis are becoming more common History is important to determine if testing is helpful Skin prick tests are informative if allergen is known Epipen should be prescribed if at risk of anaphylaxis May need to review need for testing/epipen at later date
Thank you
REFERENCES V Baral, J Hourihane. Food Allergy in Children. Postgrad Med J 2005;81:693-701 A Clark, P Ewan. Food Allergy in Childhood. Arch Dis Child 2003;88:79-81 C Macdougall, A Cant, A Colver. How Dangerous is Food Allergy in Childhood? The Incidence of Severe and Fatal Allergic Reactions Across the UK and Ireland. Arch Dis Child 2002;86:236-239 S Bock, A Munoz-Furlong. Fatalities due to anaphylactic reactions to foods. J Allergy Clin Immunol 2001;107:191-3 H Sampson. Food Allergy. JAMA 1997;278:1888-94