Allergy Diagnosis and Treatment Flashcards
What is allergy?
Inappropriate/harmful response to foreign substances that are otherwise not harmful to body
Mediated largely by IgE
What is an allergen?
Generally protein that elicits IgE response in allergic individuals
What are some symptoms of an allergy if the allergen is inhaled?
Rhinitis
Asthma
What are some symptoms of an allergy if the allergen comes into contact with the skin?
Acute contact urticaria
What are some symptoms of an allergy if the allergen is swallowed?
Oral allergy syndrome
Cramping/vomiting/diarrhoea
Can lead to anaphylaxis
What is considered a positive skin prick test?
3+ mm wheal
What are the advantages of a skin prick test?
Highly sensitive
In vivo exposure to allergen
Convenient
Results obtained within 20 mins
What are the disadvantages of a skin prick test?
Small potential for anaphylaxis May lack specificity due to - Sensitised by asymptomatic individuals - Irritant false positive reactions Usually need specialist clinic
What is the role of serology in the diagnosis of allergies?
Measure allergen-specific IgE
Radio-allergosorbent test (RAST) now redundant but commonly used name for other serology tests used now
What are the advantages of in vitro assays?
Availability
Safety
Specific, particularly at high level
Standardised
What are the disadvantages of in vitro assays?
May get false positives with elevated total IgE
What is the gold standard for allergy diagnosis?
Challenge tests
When are challenge tests used in the diagnosis of allergy?
When RAST and skin prick tests negative/discordant and good clinical story
What is allergen immunotherapy?
Only current allergy therapy to provide prolonged improvement/cure
Efficacy limited by side effects
Initiated and/or supervised by allergist
For what is allergen immunotherapy indicated?
Venom allergy Allergic rhinitis Mild, well controlled allergic asthma - Stable symptoms - FEV1 >70% predicted
What is sublingual immunotherapy?
Doses of allergen extract self-administered daily by patient sublingually Held for 2 mins under tongue > swallowed Effective as subcutaneous immunotherapy Minimal risk of anaphylaxis Extracts more expensive
What is anaphylaxis?
Serious allergic reaction that may cause death
Generalised serious IgE-mediated allergic reaction usually involving
- Cardiovascular
- Hypotension
- Respiratory tract
- Asthma
- Laryngeal oedema
Are atypical presentations of anaphylaxis common?
Not uncommon, particularly in very old/very young
What is the mechanism of anaphylaxis?
Massive mediator release primarily from mast cells and basophils
Vasodilation, fluid extravasation, bronchial smooth muscle contraction, mucosal oedema
Death due to
- Shock
- Hypoxaemia
What are mild symptoms of anaphylaxis?
Pruritis - Hand - Groin Urticaria Flushing Vomiting Diarrhoea
What are moderate and severe symptoms of anaphylaxis?
Angioedema - Lips - Tongue - Larynx Wheeze Asthma Hypotension Loss of consciousness
What are the main causes of fatal anaphylaxis?
Food allergy, especially nuts
Insect venom
Drugs
What are the risk factors for fatal food-related anaphylaxis?
Associated asthma Lack of self-injectable adrenaline Young adults Alcohol Extreme sensitivity
What are the main insect venom allergies?
Bees
European wasps
Jumper ants
In whom are latex allergies mainly seen?
Healthcare workers
Spina bifida patients
What symptoms are latex allergies most commonly associated with?
Irritant/contact dermatitis
Which allergens can latex allergens be cross-reactive with?
Banana
Avocado
Kiwi
Which drugs are common causes of drug allergies?
Antibiotics - Penicillins - Cephalosporins Radiocontrast agents Anaesthetics - Muscle relaxants NSAIDs Natural medicines
What are the principles of long-term therapy in allergy management?
Avoidance
Education on action plan
Medical alert bracelet
Why should IV adrenaline be avoided?
Associated with significant adverse effects > best to deliver IM
Is prescription of an adrenaline auto-injector recommended for a drug allergy?
No, but would be good to have on hand
What is the most common cause of anaphylactic deaths?
Medications
What are non-specific treatments for allergies?
Antihistamines Corticosteroids Adrenaline Leukotriene antagonists Anti-IgE Abs
