top of page

Allergy and Anapylaxis

An allergy is an IgE-mediated Type I Hypersensitivity reaction. During this reaction, the allergen binds to Specific IgE on Mast cells after a previous sensitisation phase, leading to cross-linking and eventual degranulation e.g. histamine release.


Atopy = Genetic tendency to produce specific IgE antibodies on exposure to common environmental antigens e.g. pollen, dust mites, food, cat etc.


Investigations

In the history, it's important to find out the:

  • Time course of the allergic reaction

  • Triggers

  • Seasonality of symptoms

  • Location where symptoms are worse (indoors, outdoors etc)

  • Hx of Atopy i.e. eczema, asthma, allergic rhinitis (hayfever)


Specific IgE is measured via either:

  • Blood Test (BT) - Direct

  • Skin Prick Testing (SPT) - Indirect

    • Specific IgE > 0.35 = Positive/IgE Sensitisation

    • Total IgE (kU/L) - Increased = Atopic tendency

N.B. These tests only confirms IgE Sensitisation, which may not be associated with an actual allergy.

Anaphylaxis

This presents with:

  • Widespread urticaria (hives)

  • Angioedema

  • Wheeze

  • Bronchospasm

  • Abdominal pain, N+V, Diarrhoea

  • Tachycardia

  • Hypotension


Management:

  • Remove trigger

  • Call for help

  • A-E assessment

  • Give O2

  • IM Adrenaline (1:1000)

  • Fluid resuscitation if hypotensive


A Serum Tryptase is used to confirm the diagnosis.


N.B. Tryptase level taken within 15 mins to 3 hours after onset of anaphylaxis with repeat level done at least 24 hours after resolution of anaphylaxis symptoms.


bottom of page