Food Allergy Flashcards
(24 cards)
Name 5 non-immunological adverse reactions to foods
- Enzyme deficiency
- Histamine reactions e..g strawberries, salami, tuna, salmon
- Toxicity e.g. scrombotoxin poisoning
- Food sensitive migraine
- Flushing in acne rosacea
Give 2 examples of enzyme deficiencies which give rise to adverse food reactions
Are there any populations who experience these more?
- Lactase deficiency (acquired/inheritied)
- Alcohol dehydrogenase deficieny
- South East Asians experience flushing reaction to alcohol
How are non-immunological food reactions diagnosed and treated?
Diagnosis is clinical
- No validated scientific tests
Management is dietary
What is a food intolerance?
All detrimental reactions to food that are non-IgE mediated
- Explains a range of symptoms in terms of food sensitivities
- Commonest is irritable bowel syndrome-type symptoms
- No validated tests- dietary approach
Describe the early phase allergic reaction
- In allergic individuals, exposure to allergens leads to rapid development of symptoms
- Reactions develops within seconds/minutes of expsosure
- Results from binding of allergens to preformed IgE antibodies on the surface of mast cells and basophils
Describe the events that follow mast cell IgE ligation
- IgE binds its specific allergen
- Cross linking of IgE antibodies by allergen leads to clustering of FcεR1 receptors
- The intracellular portion of the receptor becomes phosphorylated
- The resulting intracellular cascade leads to cellular activation
- Mast cell ‘degranulates’ releasing histamine, tryptase and other preformed mediators
State 5 pharmacological effects of mast cell mediators
Skin/mucus membranes
- Hives: wheal and flare
- Angioedema: swelling
Nose
- discharge, sneezing
Eyes
- Conjunctivitis
Gut
- Oral allergy, vomiting, diarrhoea
Lung
- Wheeze
Describe how degradation of the mast cell can lead to the occlusion of the vocal chords
- Histamine in deeper tissue areas–> swelling
- In vocal chords this can cause airway compromise and stridor (LIFE THREATENING)
How do you approach the management of a type 1 allergy
- Think about the potential triggers
- Carry out a test to confirm e.g. skin prick, serology, challenge
- Identify the risk
- Create an avoidance plan and an emergency plan
What are the GI symptoms of IgE mediated food allergy?
- Nausea, vomiting, diarrhoea
- Oral allergy (itching, tingling, irritation): local allergic symptoms in mouth
What are the cutaneous symptoms of IgE mediated food allergy?
Hives
Angioedema
What are the respiratory and CV symptoms of IgE mediated food allergy?
RESP
- Upper airway symptoms: wheezing, rhinitis
- Lowe airway symptoms:
CV
- Dizziness, collapse due to hypotension
What are the general features of true food allergy`?
- Rapidly follows (consumption of) food
- Generally multi systemic
- Recedes rapidly
- Reproducible
- Only rarely implicates multiple food sources
- (positive testing)
Describe in vivo allegen testing
Test for allergen-specific IgE
- Drops of allergen applied to skin
- Top layer of epidermis is punctured with lancet which allows allergen to contact cutaneous mast cells
- If mast cell are sensitised to the allergen, degranulation produces an itchy wheal and flare response <15minutes
- Requires positive and negative controls for validation
How do you request a RAST/Allergen specific IgE immunoassay
Send a clotted sample to immunology lab
- Ask SPECIFICALLY
“Specific IgE to…”
(Known allergen stick to solid phase, if specific IgE present they bind. Wash. A detection antibody is added which binds to Fc portion of bound IgE)
Compare skin prick testing against serology in the following parameters:
a. Availability
b. Speed of results
c. Range of allergens that can be tested
d. Effect of medication
e. Effect of skin conditions
f. Cost
g. No. of tests required for numerous antigens
h. Reproducibility
SKIN PRICK TEST
- requires clinic infrastructure, not easily available
- results same day
- smaller range of allergens
- affected by medication
- require normal skin for testing
- similar costs to do multiple tests
- multiple tests requires multiple punctures, which is poorly tolerated by toddlers
- operator dependent
SEROLOGY
- easily available via lab
- results in days-weeks
- unaffected by medication and skin conditions
- multiple test are expensive
- multiple test can be performed with one sample
- lab dependent, but they are better at standardisation and QC
How would you manage a known IgE mediated peanut allergy ?
- Adrenaline pen training
- Peanut avoidance, however risk of accidental exposure higher with selective nut avoidance
Describe primary allergens
- unique to allergen source
- sensitisation= severe rise of severe reactions
- dont produce false positives for other allergens
- positive by serology and skin test
Describe pan-allergens
- found in multiple allergen sources
- usually milder reactions or no reactions
- skin tests less sensitive compared to serology
What are the pitfalls of food allergy testing?
- The native allergens in testing are natural products and contain a mix of pan-allergens and primary allergens; the result reflects IgEs directed at either/both of theses
- This can create false positives, or negative results
- Sensitisation to pan allergen/primary allergens creates different risk profile
The peanut has different surface antigens
What are the different Ara h proteins?
Ara h 1,2,3 = storage proteins
Ara h 8= birch pollen homolog
What is birch oral allergy syndrome?
Presentation?
What are the common stimulants in the UK?
- Commonest UK adult food allergy
- IgE directed against major birch pollen allergen (Bet v 1) cross reacts with homologous proteins in plant derice foods (e.g. Ara h 8)
- Oral itching upon exposure to raw fruit, nuts and vegetables
- Doesnt progress to anaphylaxis
- Pollen (mainly birch) and rosaceae fruits
Describe false negatives and positives when applied to birch oral allergy syndrome
- Patients who are sensitised to birch pollen often sensitised to nuts and fruits by serology- but dont always have symptoms (false positive)
- Patients with syndrome typically test negative despite allergy (false negative)
How can you manage panic attacks secondary to food allergy?
Cognitive behavioural therapy
