Allergy & Immunology
AKT High-Yield Breakdown
Allergy and immunology covers a broad spectrum from common allergic rhinitis and food allergy to life-threatening anaphylaxis and rare primary immunodeficiencies. The AKT tests the classification of allergic reactions, management of chronic allergic conditions, penicillin allergy de-labelling, and when to suspect immunodeficiency.
What You'll Learn
Master Gell and Coombs hypersensitivity classification, allergic rhinitis treatment hierarchy, hereditary angioedema (C1-esterase inhibitor deficiency), penicillin cross-reactivity rules, food allergy IgE versus non-IgE distinction, and the red flags that should prompt immunodeficiency investigation.
Practise Allergy & Immunology MCQs
From Gell and Coombs hypersensitivity types and anaphylaxis management to hereditary angioedema, penicillin cross-reactivity, and post-splenectomy vaccination — tackle focused MCQs across the full Allergy & Immunology curriculum.
Hypersensitivity Reactions
The Gell and Coombs classification of hypersensitivity is fundamental and directly tested in the AKT. Understanding the mechanism predicts the timing and clinical features of each reaction.
- Type I — IgE-mediated (immediate): mast cell degranulation → histamine, prostaglandins, leukotrienes; occurs within minutes; anaphylaxis, allergic rhinitis, asthma, urticaria, food allergy; examples: penicillin, peanut, bee sting
- Type II — Antibody-mediated cytotoxic: IgG/IgM against cell surface antigens → complement activation or phagocytosis; examples: autoimmune haemolytic anaemia, ITP, Goodpasture's, haemolytic disease of newborn, transfusion reactions
- Type III — Immune complex-mediated: IgG complexes deposited in tissues → complement → inflammation; occurs 4–10 hours; serum sickness, hypersensitivity pneumonitis (farmer's lung), post-streptococcal GN, SLE, cryoglobulinaemia
- Type IV — Delayed (cell-mediated, T-cell): T-lymphocyte mediated; occurs 24–72 hours; contact dermatitis (nickel, latex), TB (Mantoux), graft rejection, coeliac disease, Stevens-Johnson syndrome
The key distinguishing feature between types is timing: Type I = minutes; Type III = hours (4–10); Type IV = days (24–72). Serum sickness (Type III) classically occurs 7–14 days after drug or antiserum exposure.
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