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Immunology > 2.1.2 Introduction to Food Allergy II > Flashcards

2.1.2 Introduction to Food Allergy II Flashcards

1
Q

What is food intolerance?

A

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

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2
Q

What is the prevalence of food allergies?

A

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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3
Q

What are the two types of adverse food reaction?

A

Non-immune mediated
Immune mediated

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4
Q

What can cause non-immune mediated adverse food reactions?

A

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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5
Q

What are some examples of IgE mediated adverse food reactions?

A

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

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6
Q

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

A

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

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7
Q

Fill in the table

A
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8
Q

Clinical presentation IgE mediated vs non-IgE mediated

A

IgE
- Skin
- GI
- Respiratory
- CVS

Non-IgE
- Skin
- GI

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9
Q

Skin symptoms IgE vs non-IgE

A

IgE
- Pruritis
- Erythema
- Acute urticaria
- Acute angioedema

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

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10
Q

GI symptoms IgE vs non-IgE

A

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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11
Q

Respiratory and CVS symptoms of IgE

A

Upper respiratory- blocked nose, sneeze, itch

Lower respiratory- wheeze, cough, SOB

CVS-pallor, drowsy, hypotensive

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12
Q

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

A

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

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13
Q

What is pollen food syndrome?

A

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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14
Q

What is food associated exercise induced anaphylaxis?

A

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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15
Q

What is proctolitis?

A

Non-IgE mediated

Passage of bright red blood in mucousy stools in asymptomatic infants

Caused by milk (breast milk too)

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16
Q

What is enterocolitis?

A

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

17
Q

What is eosinophilic oesophagitis?

A

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

18
Q

What is food protein induced enterocolits syndrome?

A

Non-IgE

Primarily affects infants

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

Often misdiagnosed as sepsis

19
Q

How does temperature affect cow’s milk?

A

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

20
Q

How does temperature affect egg white?

A

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

21
Q

How does temperature affect peanuts?

A

Allergenicity increased if dry roasted

Decreased if boiled or fried

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

22
Q

How does temperature affect fish?

A

Protein very heat stable, allergenicity not affected

Reduced allergenicity in canning

23
Q

How does temperature affect apple?

A

Fruit proteins are heat sensitive

Patients with pollen food syndrome can eat processed apple

24
Q

What is allergic cross reaction?

A

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

25
Q

How do you take a food allergy history?

A

EATERS
Exposure- when eaten, handled raw food, kissing etc.
Allergen- common allergens, milk, eggs, nuts, shellfish etc.
Timing- most IgE-immediate, non IgE-delayed
Environment- weaning, most rections with first exposure, eating away e.g. parties, holiday etc.
Reproducibility- symptoms should go away with removal, re-exposure-same symptoms
Symptoms

26
Q

What screening tests are used to detect food allergies?

A

IgE mediated Food Allergy
- Skin prick tests
- Blood specific IgE

IgE and non-IgE
- Elimination diet

27
Q

Outline the mechanism of sensitisation

A
  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
28
Q

Outline the mechanism of allergy in T1HSRs

A
  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.
29
Q

How do you carry out a skin-prick test?

A

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

30
Q

Label the image of IgE antibody production

A
31
Q

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

A

SPT
Detects IgE bound to skin mast cells

sIgE
Detects IgE in the blood

32
Q

What do allergy tests detect?

A

Sensitisation NOT allergy

33
Q

When is an allergy test positive or negative?

A

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)

34
Q

What is sensitivity?

A

Proportion of people with the disease who test positive

people who are positive-positive

Remember using N in sensitviity, N=negative, then opposite

35
Q

What is specificity?

A

Proportion of people without the disease who test negatively

people who are negative-negative

Remember using the P in specificity P=postive then opposite

36
Q

What is positive predictive value?

A

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)

37
Q

What is negative predictive value?

A

Change that someone who is negative is negative

True negatives/ (True negatives + False negatives)

38
Q

What is the sensitivity and specificity for food allergy tests?

A

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

39
Q

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

A

Food exposure test

Immunology (14 decks)

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