3. Food Allergy

Question 1

What is the definition of an allergy?

Answer 1

A hypersensitivity reaction initiated by specific immuno- logical mechanisms. This can be IgE mediated (e.g. peanut allergy) or non-IgE mediated (e.g. milk allergy).

Question 2

What is an allergen?

Answer 2

Any substance stimulating the production of IgE or a cellular immune response. Usually a protein, but can be carbohydrates (much less common).

Question 3

What is sensitivity?

Answer 3

Normal response to a stimulus.

Question 4

What is hypersensitivity?

Answer 4

An abnormally strong response to a stimulus.

Question 5

What is sensitisation?

Answer 5

Production of IgE antibodies after repeated exposure to an allergen.

Question 6

What is atopy?

Answer 6

A tendency to produce IgE antibodies in response to ordinary exposure to potential allergens. Strongly associated with asthma, rhinitis, eczema and food allergy.

Question 7

What is anaphylaxis?

Answer 7

A serious allergic reaction with bronchial, laryngeal and cardiovascular involvement that is rapid in onset and can cause death.

Question 8

Which allergies tend to present in younger children? And which in older?

Answer 8

Younger - eczema, food allergy.
Middle - asthma.
Older - rhinitis.

Question 9

How is a food intolerance different to a food allergy?

Answer 9

Food intolerance is an adverse response to food that does not involve the immune system. Food allergy is an adverse health affect arising from a specific immune response that occurs on food exposure.

Question 10

What is urticaria with angioedema?

Answer 10

Acute hives and swelling with respiratory but not gastrointestinal or CVS symptoms.

Question 11

What is food-associated exercise induced anaphylaxis?

Answer 11

Food triggers anaphylaxis only if ingestion is followed temporally (within 2 hours) by exercise.

Question 12

What is pollen food syndrome?

Answer 12

Pruritus and mild oedema confined to the oral cavity (lips, tongue, mouth and throat) uncommonly progressing. Associated with hay fever (raw fruit and vegetables)

Question 13

What is protocolitis?

Answer 13

Passage of bright red blood in mucousy stools in otherwise asymptomatic infants. (milk, through breast feeding)

Question 14

What is enterocolitis?

Answer 14

Multiple and varying gastrointestinal symptoms including feed refusal, persistent vomiting, abdominal cramps, loose and frequent stools and constipation. (milk, eggs, wheat).

Question 15

What is eosinophilic oesophagitis?

Answer 15

Symptoms from oesophageal inflammation and scarring of feeding disorders, reflux symptoms, vomiting, dysphagia and food impaction. (milk, eggs, wheat).

Question 16

What is food protein-induced enterocolitis syndrome?

Answer 16

Primarily affects infants. Profuse vomiting leading to pallor, lethargy and possibly shock; diarrhoea in 25%. Increased WCC, so careful isn’t sepsis. (milk, soya, rice, wheat, meat).

Question 17

Is immediate onset or delayed onset food allergy IgE mediated?

Answer 17

Immediate - IgE mediated.

Delayed - non IgE mediated.

Question 18

Give 3 presentations of immediate-onset (IgE mediated) food allergy

Answer 18

Urticaria/angioedema.
Anaphylaxis.
Food-associated exercise induced anaphylaxis.
Pollen food syndrome.

Question 19

Give 3 presentations of delayed-onset (non-IgE mediated) food allergies

Answer 19

Protocolitis.
Enterocolitis.
Eosinophilic oesophagitis.
Food protein-induced enterocolitis syndrome.

Question 20

Which food allergies are diagnosed more in infancy, early childhood, and adolescence?

Answer 20

Infancy - milk, egg, peanut.
Early childhood - soya, wheat, tree nuts, fish, shellfish, kiwi, sesame.
Adolescence - fresh fruit and vegetables (pollen food syndrome).

Question 21

What common allergens are less allergenic when cooked?

Answer 21

Cow’s milk, egg white, apples.

Question 22

Why can food processing (eg by cooking with other ingredients such as wheat) make an allergen non-allergenic?

Answer 22

Food processing destroys conformational epitopes which were causing the reaction.

Question 23

What type of food allergy has immediate symptom onset?

Answer 23

Immediate (5-30 minutes) - IgE mediated.

Delayed (hours or days) - non IgE mediated.

Question 24

Do IgE mediated or non-IgE mediated food allergies have more vague symptoms?

Answer 24

Non-IgE mediated more vague and common with other conditions.

Question 25

How would you diagnose an IgE mediated food allergy?

Answer 25

Skin prick test.

Immunoassay to detect allergen-specific IgE.

Question 26

How would you diagnose a non-IgE food allergy?

Answer 26

Elimination diet.

Question 27

What does a skin prick test determine?

Answer 27

Presence of sensitivity not allergy.

Question 28

What does the size of the weal in a positive skin prick test reaction correlate with?

Answer 28

Likelihood of allergy - >8mm allergy very likely (95% true predictive value). Size does not correlate with or predict severity of allergic reaction.

Question 29

Give 3 ways of managing a food allergy.

Answer 29

Anticipatory testing (eg test for cross-reactive allergens or potential future allergens to minimise reactions and dietary exclusions).
Dietetic advice for dietary exclusions.
Prescription of emergency medicine where indicated.
Early food introductions in infancy and reintroduction where allergy known to resolve.
Desensitisation to food allergens )eg baked milk and egg in re-introductions).
Oral food challenges for diagnostic verification.