Allergy Flashcards
Allergy
Hypersensitivity of immune system to allergens
Allergen
Protein that immune system recognises as foreign and potentially harmful
Leading to allergic immune response
Types of antigen
Antigens
Proteins that can be recognised by immune system
Atopy conditions
Eczema Asthma Hay fever Allergic rhinitis Food allergies
What are the two main contributors to a child developing an allergy to a food?
Break in skin (eczema or skin infection), allows allergens from environment to cross skin and react with immune system
Child doesn’t have contact with that allergen from GI tract, absence of GI exposure to allergen
Hypersensitivity conditions
Asthma Atopic eczema Allergic rhinitis Hay fever Food allergies Animal allergies
Coombs and Gell classification hypersensitivity
TY1: IgE
TY2: IgG and IgM
TY3: immune complex
TY4: T lymphocytes
TY1 hypersensitivity
IgE antibodies to a specific allergen
Trigger mast cells and basophils to release histamine and other cytokines
Immediate reaction
Food allergy
TY2 hypersensitivity
IgG and IgM antibodies
React to allergen and activate complement system
Direct damage to the local cells
Examples: HDN, transfusion reactions
TY3 hypersensitivity
Immune complexes accumulate and causes damage to local tissues
SLE, rheumatoid arthritis, Henoch-Schonlein purpura
TY4 hypersensitivity
Cell mediate hypersensitivity
T lymphocytes
T cells inappropriately activated
Causing inflammation and damage to local tissues
Organ transplant rejection and contact dermatitis
History of allergy
Timing after exposure to allergen
Previous and subsequent exposure and reaction to allergen
Symptoms of rash, swelling, breathing, difficulty, wheeze and cough
Previous personal and FH of atopic conditions and allergies
Investigations in allergy
Skin prick testing: sensitisation
RAST testing: sensitisation
Food challenge testing: gold standard for diagnosing allergy
Skin prick testing
Fresh needle, water control, histamine control
After 15 minutes, size of wheals to each allergen are assessed and compared to the controls
Patch testing
Used to diagnose allergic contact dermatitis
Not helpful for food allergies
After 2-3 days assess skin reaction to patch
RAST testing
Measures total and allergen specific IgE quantities in patients blood sample
Allergy management
Establish and avoid correct allergen
Avoid foods that trigger reactions
Regular hoovering and changing sheets and pillows if there is a dust mite allergy
Staying indoor where pollen count is high
Prophylactic antihistamines where contact is inevitable
Adrenalin auto-injector for patients at risk of anaphylaxis
Immunotherapy
Treatment following exposure of allergen
Antihistamines (cetirizine)
Steroids
IM adrenaline
Anaphylaxis presentation
History of exposure Urticaria Itching Angio-oedema Abdominal pain
SoB Wheeze Swelling of larynx, causing stridor Tachycardia Lightheadedness Collapse
Anaphylaxis principles of management
Airway: secure airway
Breathing: provide oxygen if required, salbutamol can help with wheezing
Circulation: IV fluid bolus
Disability: lie patient flat to improve cerebral perfusion
Exposure: look from flushing, urticaria, angio-oedema
Medications to treat anaphylaxis
IM adrenaline
Antihistamines: oral chlorphenamine or cetirizine
Steroids, hydrocortisone
After anaphylaxis
Biphasic reaction
Measure serum mast cell tryptase within 6 hours
Train parents in BLS
Adrenalin auto-injector
Adrenalin auto-injector indications
Anaphylaxis reactions Asthma requiring inhaled steroids Poor access to medical treatment Adolescents Nut/insect sting allergies Significant co-morbidities
How to use adrenalin auto-injection
Epipen
Remove blue cap Grip device needle end is orange Administer injection, hold for 3s Remove device and massage for 10s Phone ambulance Second dose after 5 mins
How to use Jext epipen
Remove yellow cap Grip device needle end is black Administer injection, hold for 10s Remove device and massage for 10s Phone ambulance Second dose after 5 mins
Types of allergic rhinitis
Seasonal, hay fever
Perennial, house dust mite allergy
Occupational
Allergic rhinitis presentation
Runny, blocked and itchy nose
Sneezing
Itchy, red and swollen eyes
Allergic rhinitis triggers
Tree pollen or grass
House dust mites and pets
Management of allergic rhinitis
Avoid trigger Hoover Stay indoors during high pollen counts Minimise contact with pets Oral antihistamines Nasal corticosteroid sprays: fluticasone, mometasone Nasal antihistamines
Non-sedating anti-histamines
Cetirizine
Loratadine
Fexofenadine
Sedating antihistamines
Chlorphenamine (piriton)
Promethazine
Cows milk protein allergy
Typically affects <3 years IgE mediated (reaction occurring within 2 hours) or non-IgE mediated (over several days)
Risk factors: formula-fed babies, personal or FH of other atopic conditions
Cows milk protein allergy presentation
Presents before 1 year of age
Apparent when weaned from breast milk to formula milk
Bloating and wind
Abdominal pan
D/V
Allergi symptoms in cows milk protein allergy but not cows mill intolerance
Management of Cow’s milk protein allergy
Breast feeding mothers should avoid dairy Hydrolysed formulas: proteins broken down Elemental formulas (amino acids) Every 6 months try infants on milk ladder
