2.1.2 Introduction to Food Allergy II Flashcards by Nat Perris

What is food intolerance?

Numerous suspected adverse responses to food that do not involve the immune system

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What is the prevalence of food allergies?

170 foods can cause IgE mediated reactions

Milk, egg and peanut are the most common

Self-reported allergy is 6x than proven allergy

Proven allergy more prevalent in children, 6% kids vs 2% adults

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What are the two types of adverse food reaction?

Non-immune mediated
Immune mediated

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What can cause non-immune mediated adverse food reactions?

Food characteristics
- Pharmacologic e.g. caffeine
- Toxic e.g. scromboid fish toxin (when fish gets cold and is reheated and then cools again bacteria grows)

Host characteristics
- Metabolic e.g. lactose intolerance
- Psychological e.g. anxiety, food aversion

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What are some examples of IgE mediated adverse food reactions?

Acute urticaria/angioedema
Anaphylaxis
Pollen food syndrome
Food-associated exercise-induced anaphylaxis

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What are some exampels of non-IgE immune mediated causes of adverse food reactions?

Proctocolitis
Entercolitis
Eosinophylic oesophagitis
Food protein induced enterocolitis syndrome (FPIES)

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Fill in the table

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Clinical presentation IgE mediated vs non-IgE mediated

IgE
- Skin
- GI
- Respiratory
- CVS

Non-IgE
- Skin
- GI

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Skin symptoms IgE vs non-IgE

IgE
- Pruritis
- Erythema
- Acute urticaria
- Acute angioedema

Non-IgE
- Pruritis
- Eczema
- Atopic eczema (does not respond adequately to treatment)

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GI symptoms IgE vs non-IgE

IgE
- Angioedema of lips, tongue and palate
- Oral pruritis
- Nausea/vomiting
- Diarrhoea
- Colicky abdominal pain

Non-IgE
- Food refusal or aversion
- GORD
- Abdominal pain, infantile colic
- Loose/infrequent stools
- Constipation
- Perianal redness
- Pallor and tiredness
- Faltering growth

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Respiratory and CVS symptoms of IgE

Upper respiratory- blocked nose, sneeze, itch

Lower respiratory- wheeze, cough, SOB

CVS-pallor, drowsy, hypotensive

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What do we do when the suspected cause of eczema is due to a food allergy?

Rare
- Exclude for diet for 6 weeks
- If there is no change, this is not the cause

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What is pollen food syndrome?

IgE mediated food allergy

Pruritus and mild oedema confised to oral cavity (lips,tongue,mouth and throat)
can progress to systemic symptoms

Associayed with pollen sensitisation +/- symptoms

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What is food associated exercise induced anaphylaxis?

Food triggers anaphylaxis only if ingestion is followed
within 2-4 hours by exercise (even mild e.g. walking to school)

Wheat,shellfish, celery

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What is proctolitis?

Non-IgE mediated

Passage of bright red blood in mucousy stools in asymptomatic infants

Caused by milk (breast milk too)

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What is enterocolitis?

Multiple and varying GI symptoms including:
- Food refusal
- Persistent vomiting
- Abdominal cramps
- Loose and frequent stools
- Constipation

What is eosinophilic oesophagitis?

Symptoms from:
- Oesophageal inflammation and scarring of feeding disorders
- Relfux symptoms
- Vomitting
- Dysphagia
- Food impaction

What is food protein induced enterocolits syndrome?

Non-IgE

Primarily affects infants

Profuse vomiting 2 hours after ingesting leading to:
- Pallor
- Lethargy
- Shock
- Infrequent diarrhoea

Often misdiagnosed as sepsis

How does temperature affect cow’s milk?

Casein is more heat resistant than whey

Forms bonds in a food matrix to reduce availability and allergenicity

70% of milk allergic kids can tolerate baked milk

Beta lactam splits, casein doesn’t

How does temperature affect egg white?

4 major proteins in egg white

All major proteins except ovomucoid are heat labile

Well-cooked egged is less allergenic than raw egg

70% of egg allergic kids can tolerate baked egg

How does temperature affect peanuts?

Allergenicity increased if dry roasted

Decreased if boiled or fried

May account for higher prevalence of allergy in western vs asian populations

How does temperature affect fish?

Protein very heat stable, allergenicity not affected

Reduced allergenicity in canning

How does temperature affect apple?

Fruit proteins are heat sensitive

Patients with pollen food syndrome can eat processed apple

What is allergic cross reaction?

If a food has a similar structure to something you are allergic to, it can cause an allergic reaction

e.g. cow’s milk and goat’s milk

How do you take a food allergy history?

**EATERS** **E**xposure- when eaten, handled raw food, kissing etc. **A**llergen- common allergens, milk, eggs, nuts, shellfish etc. **T**iming- most IgE-immediate, non IgE-delayed **E**nvironment- weaning, most rections with first exposure, eating away e.g. parties, holiday etc. **R**eproducibility- symptoms should go away with removal, re-exposure-same symptoms **S**ymptoms

What screening tests are used to detect food allergies?

**IgE mediated Food Allergy** - Skin prick tests - Blood specific IgE **IgE and non-IgE** - Elimination diet

Outline the mechanism of sensitisation

1. Food allergen presented to the **T-cell** 2. **TH2-skewed** immune response commits **B-cells** to **IgE production** 3. Allergen-specific IgE binds to **high-affinity receptors** on mast cells and basophils

Outline the mechanism of allergy in T1HSRs

1. Allergen exposure in sensitised individual. 2. Allergens cross-link receptor bound IgE – activate mast cells and basophils. 3. Mediator releases leukotrienes and cytokines. 4. ALLERGY SYMPTOMS.

How do you carry out a skin-prick test?

Sterile prick lancet releases potential allergens into skin Wait for 15 minutes Positive tests produces wheals and flares **Can test multiple allergens at the same time**

Label the image of IgE antibody production

What are the differences between skin prick tests and allergen spcific IgE tests?

**SPT** Detects IgE bound to skin mast cells **sIgE** Detects IgE in the blood

What do allergy tests detect?

Sensitisation **NOT allergy**

When is an allergy test positive or negative?

Noraml range 0.00-0.35 kU/L Negative test (<=0.35) Positive(>0.35) If a wheal is 8mm or bigger, or sIgE is 15kU/L or more, specificity of 95% (allergy is very likely present)

What is sensitivity?

Proportion of people with the disease who test positive people who are positive-positive Remember using N in sensitviity, N=negative, then opposite

What is specificity?

Proportion of people without the disease who test negatively people who are negative-negative Remember using the P in specificity P=postive then opposite

What is positive predictive value?

Chance that someone who is positive is actually positive So, if you have 10 people and test for HepB, if 8 are positive and 2 are negative but they all test positively there is a PPV of 0.8 True positives/ (True positives +False positives)

What is negative predictive value?

Change that someone who is negative is negative True negatives/ (True negatives + False negatives)

What is the sensitivity and specificity for food allergy tests?

High sensitivity Poor specificity False positives are more likely to occur if there are multiple tests done without a poisitive allergy focused history If the history is allergy focused and positive, more likely to get true postivies and true negatives

How do you confirm a positive skin prick test or sIgE?

Food exposure test