1. Food allergies
By Phil Byass, 4th Year, HYMS
Wednesday, 03 October 2012 1

2. 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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3. 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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4. 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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5. 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 5

6. 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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7. IgE vs non-IgE mediated food allergy
NO ANAPHYLAXIS!!
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8. 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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9. 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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10. Examination
• Less important than thorough history
• Check nutritional status
• Check signs of atopy
• Rule out other causes
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11. 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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12. Wednesday, 03 October 2012 12
RAST ratings

13. 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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14. 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
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15. Anaphylaxis life-
threatening from
laryngeal oedema,
bronchoconstriction
and shock!
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16. Prognosis
• Most ‘grow out’ of food allergy to eggs, milk,
wheat and soya
• Sensitivity to peanuts, seafood, fish and tree
nuts rarely lost
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