Food allergy Flashcards
Examples of non-immunological causes of adverse reactions to foods [5]
Enzyme deficiency
- Lactase
- Alcohol dehydrogenase
Histamine reactions to certain foods
- Strawberries
- Salami
- Tuna
- Salmon
Toxic reaction
- Scrombotoxin
Food-sensitive migraine
Acne flushing
Immunological process of Type 1 allergy
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.
Effects of histamine release in Ig-E mediated allergy
Wheel and flare
Angioedema
Runny rose/ sneezing
Gut symptoms: vomiting, diarrhoea
Symptoms of Ig-E mediated allergy
- General
- Gut
- Skin
- Lungs
- CV
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)
Skin prick testing
- Procedure
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).
RAST test
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.
Compare skin prick and serology testing [6]
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.
Management of food allergy
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?)
Birch pollen allergy syndrome
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.
Management of pan-allergy
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