Food allergy Flashcards

1
Q

Examples of non-immunological causes of adverse reactions to foods [5]

A

Enzyme deficiency

  • Lactase
  • Alcohol dehydrogenase

Histamine reactions to certain foods

  • Strawberries
  • Salami
  • Tuna
  • Salmon

Toxic reaction
- Scrombotoxin

Food-sensitive migraine

Acne flushing

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2
Q

Immunological process of Type 1 allergy

A

IgE-Ab mediated reaction due to exposure to allergens

  • IgE receptors have already been pre-formed to allergens.
  • Fc region of IgE bound on mast cell receptors (FcER1) and basophils.
  • Allergens specific to IgE binds to Ab site and causes cross linking of FcER1 receptors= release of histamine.
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3
Q

Effects of histamine release in Ig-E mediated allergy

A

Wheel and flare
Angioedema

Runny rose/ sneezing

Gut symptoms: vomiting, diarrhoea

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4
Q

Symptoms of Ig-E mediated allergy

  • General
  • Gut
  • Skin
  • Lungs
  • CV
A

General

  • Occurs rapidly after exposure (within minutes)
  • Recedes rapidly
  • Reproducible
  • Multi-system reaction
  • Multiple food sources are rarely implicated

Gut

  • Diarrhoea/ vomiting
  • Oral: itching, tingling

Skin
- Hives, angioedema

Lungs
- Upper and lower tract symptoms

CV
- dizziness, collapse (low BP)

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5
Q

Skin prick testing

- Procedure

A

Epidermis punctured with a lancet after allergen has been added.

Observe for 15 mins for ‘wheel and flare’ reaction.
- Compare with control (histamine and nothing).

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6
Q

RAST test

A
Radioallergosorbent test (Blood allergy test)
- Although, not really radio-labelled anymore.
  • Patient’s serum sample is added to allergen. If IgE-specific ab to allergen are in serum, will be bound to allergen.
  • Labelled anti-human IgE Ab is then added to sample, If Ab binds to allergen, tagged ab is able to identify it.
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7
Q

Compare skin prick and serology testing [6]

A

Time
- Skin prick shows results very quickly, serology takes weeks/days.

Medication
- Skin prick affected by anti-histamines, serology not.

Number of tests
- Skin prick requires multiple punctures to test multiple allergens, immunoassay only requires one sample.

Method
- Skin prick operator-dependent, serology is more lab dependent and specific/ sensitive

Price
- Skin prick much cheaper than serology

Availability
- Skin prick only available in certain clinics, but serology can be done almost any time in a lab.

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8
Q

Management of food allergy

A

Primary allergy (type 1)

  • Asses risk: level of sensitisation, severity of reaction, medical history
  • Avoidance and emergency plan (adrenaline pen)–> carry 2 devices and training to use.

Pan-allergy sensitisation

    • Found in multiple allergen sources, can produce false-positives for other allergens.
  • Milder/ No reactions
  • Less sensitive to skin test
  • birch pollen homolg (ara h 8?)
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9
Q

Birch pollen allergy syndrome

A

Bet V 1

  • Homologous with Ara h 8
  • Cross reactivity of IgE with Bet V 1 causes birch pollen allergy syndrome
  • Tends to be rosaceae fruits

Tends to have oral symptoms after eating raw fruits/nuts/ veg

  • Itching, tingling.
  • Does not progress to anaphylaxis

Positive serology, negative skin prick.

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10
Q

Management of pan-allergy

A

Avoid exposure to main allergen but accidental exposure is not dangerous
- Not required for epipen if reaction not severe

Offer peanut challenge to build tolerance

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