Food allergy

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Food allergies

By Phil Byass, 4th Year, HYMS

Wednesday, 03 October 2012

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Epidemiology

• More often in atopic individuals (hayfever, eczema, asthma)

• 5% of young children and 3-4% of adults in UK• Prevalence rising, especially to peanuts!• 2% of infants will have cow’s milk protein

allergy


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Causes

• Epitope of food protein recognised as foreign and immune reaction as if bacteria or virus

• In infants: milk protein, egg and peanut• In older children: peanut, tree nut and fish• Also: Soy, shellfish and wheat proteins


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Food allergy vs intolerance

• Intolerance not immunologically mediated (see later slides)

• Food allergy always immunologically mediated

• And either classified as IgE mediated or non-IgE mediated


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IgE mediated food allergy• Acute reactions (<2 hours after exposure)

• Produce IgE abs to epitope of protein• Bind to receptors on mast cells and basophilsWednesday, 03 October 2012

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Non-IgE mediated food allergy

• No antibodies involved!• Mediated via T-cells• Delayed reaction to exposure (>2 hours)• FPIES (food-protein induced enterocolitis syndrome)

from cow’s milk and soy. Projectile vomiting, diarrhoea and FTT

• Eosinophilic oesophagitis and gastroenteritis. Nausea, abdo pain and reflux with no response to antacids

• Coeliac disease – gluten


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IgE vs non-IgE mediated food allergy

NO ANAPHYLAXIS!!


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Oral allergy syndrome

• Cross-reactivity between airborne allergens such as pollen and food

• Seasonal mucosal inflammation in response to certain foods

• Ragweed pollen & bananas/melons• Birch pollen & apples/peaches/celery


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History• Important to determine whether IgE mediated or not as

patient is at risk of anaphylaxis • Identify possible allergens – thorough food history

including preparation, additives, spices etc• Method of exposure – ingestion, handling or inhalation• Symptoms – When they started? How much food

needed? Every time food eaten? How long do they last? • Family history of allergies/atopy• Feeding history – age of weaning, formula or breast-fed

(consider mum’s diet).


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Examination

• Less important than thorough history• Check nutritional status• Check signs of atopy• Rule out other causes


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Investigations for suspected IgE mediated food allergy

• Food diary – may determine allergen• Skin prick test –lancet used to prick skin

through allergen solution and reaction evaluated after 15 minutes vs saline (-ve) vs histamine (+ve) control. Positive if wheal>2mm.

• RAST (radioallergosorbent test). Take blood. Measure allergen specific IgE – via ELISA. Radiolabelled anti-IgE added and binds to IgE. Estimated from amount of bound radioactivity in blood


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RAST ratings

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Investigations for suspected non-IgE mediated food allergy

• Trial elimination diet (2-6 weeks) to see if symptoms improve, then reintroduce after trial to see if symptoms return

• FBC – eosinophilia in 50%• Endoscopy/biopsy may show eosinophilic

invasion on microscopy


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Management

• Avoidance of food – difficult when eating out. Patients advised to check food labelling

• Dietician referral• Antihistamines if symptoms less severe• Adrenaline if severe respiratory symptoms or

anaphylaxis. Epipen and how to use it! • Medicalert bracelets or necklaces for those at high

risk of anaphylaxis• Patient/parent/carer education. Written emergency

plan helpful Wednesday, 03 October 2012

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Anaphylaxis life-threatening from laryngeal oedema, bronchoconstriction and shock!


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Prognosis

• Most ‘grow out’ of food allergy to eggs, milk, wheat and soya

• Sensitivity to peanuts, seafood, fish and tree nuts rarely lost


Food allergy

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