GPAtlas🧭 When to suspect
Anaphylaxis is a severe, life-threatening, generalised hypersensitivity reaction. It is a clinical diagnosis resting on three features:
• sudden onset
• rapid progression
• a life-threatening Airway, Breathing or Circulation (ABC) problem.
Skin and mucosal changes (urticaria, flushing, angio-oedema) accompany most cases but are absent in up to 20% – so their absence never excludes the diagnosis.
Exposure to a known allergen supports it, yet no trigger is found in around 30% (idiopathic).
Angio-oedema is self-limiting deep dermal and subcutaneous swelling (lips, tongue, eyelids, genitalia, hands, feet).
• The swelling is typically non-itchy and tight rather than the itchy weals of urticaria, and may take up to 72 hours to settle.
• The decisive question is mechanism: histaminergic (mast-cell/allergic, responds to antihistamines and adrenaline) versus bradykinin-mediated (ACE inhibitor or hereditary).
• Bradykinin-mediated swelling does not respond to antihistamines, steroids or adrenaline.
• The two primary-care priorities are to never miss evolving anaphylaxis – any ABC involvement means IM adrenaline now – and to identify and remove the trigger.
| Pattern | Recognise it by | First action |
|---|---|---|
| Anaphylaxis | • Sudden onset, rapid progression, life-threatening Airway and/or Breathing and/or Circulation problem • Skin changes usual but absent in up to 20% |
IM adrenaline now + call 999 |
| Histaminergic angio-oedema (± urticaria) | • Itchy swelling, often with weals • Mast-cell/allergic • Lips, eyelids, tongue |
• Non-sedating antihistamine • Treat as anaphylaxis if any ABC involvement |
| Bradykinin-mediated angio-oedema (ACE inhibitor or hereditary) | • Non-itchy, no weals, slower onset, face/tongue/larynx • Poor response to antihistamine, steroid and adrenaline |
• Stop the ACE inhibitor • Protect the airway • Specialist (C1-INH/icatibant) if airway threatened |
Source: Resuscitation Council UK · NICE NG258
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