Allergy and anaphylaxis Flashcards
What is allergy?
umbrella term for hypersensitivity of immune system to allergens
What are allergens?
Proteins that immune system recognises as foreign and potentially harmful
allergic immune response
What are antigens?
Proteins recognised by immune system
Atopy
predisposition to having hypersensitivity reactions to allergens
Atopy conditions
hayfever, eczema, asthma, allergic rhinitis and food allergies
Type 1 hypersensitivity
IgE antibodies to specific allergen trigger mast cells and basophils to release histamine and cytokines
immediate eg food allergy
Type 2 hypersensitivity
IgG and IgM - complement system
haemolytic disease of newborn and transfusion reactions
Type 3 hypersensitivity
Immune complexes accumulate and cause damage to local tissues eg SLE
Type 4 hypersensitivity
cell mediated by T cells
contact dermatitis and organ transplant rejection
History
timing after exposure
previous and subsequent exposure
rash, swelling, breathing difficulty, wheeze and cough
FH and personal history - atopy
3 main ways to test for allergy
skin prick testing
RAST testing - IgE
food challenge testing
What do skin prick testing and RAST testing assess?
sensitisation not allergy
Gold standard for diagnosis
food challenge testing
How is skin prick testing done?
forearm
drop of allergen eg peanut, house dust mite and pollen
water control and histamine control
15 mins, size of wheals
What is patch testing good for?
allergic contact dermatitis
RAST testing
total and allergen specific IgE
asthma and eczema
Management of allergies
establish allergen and avoid
prophylactic antihistamines
adrenalin auto-injector
immunotherapy
Treatment following exposure to allergen
antihistamine eg cetrizine
steroids eg oral prednisolone
im adrenalin
What causes anaphylaxis?
severe type 1 hypersensitivity
mast cells rapidly release histamine
key feature differentiating anaphylaxis from non-anaphylactic?
compromise of airway, breathing or circulation
Presentation of anaphylaxis
urticaria, itching, angioedema
abdominal pain
SOB, wheeze, stridor
tachycardia, collapse
ABCDE of anaphylaxis
secure the airway oxygen, salbutamol for breathing IV bolus of fluids lie patient flat to improve cerebral perfusion flushing, urticaria and angio-oedema
3 medications anaphylaxis
im adrenalin (repeat after 5 mins if required)
antihistamines eg chlorphenamine or cetrizine
steroids - IV hydrocortisone
Why should children have a period of assessment after anaphylaxis?
biphasic reactions
Confirming anaphylaxis
serum mast cell tryptase within 6 hours of event
what is tryptase?
released during mast cell degranulation
Time frame to measure mast cell tryptase
within 6 hours
Allergy risk factors to give epipen
asthma requiring inhaled steroids rural locations adolescents nut allergies co-morbidities
using adrenalin auto-injector
remove safety cap grip device in fist jab device outer thigh until click hold for 3 seconds remove and massage area 10seconds
