Angioedema has two broad mechanisms. Histamine-mediated angioedema usually comes with urticaria or itch, often follows an allergen, and responds to adrenaline, antihistamines and steroids. Bradykinin-mediated angioedema — hereditary angioedema, ACE-inhibitor angioedema and acquired C1-inhibitor deficiency — typically has no hives or itch, develops over hours, and does not respond to those drugs.
ACE-inhibitor angioedema can appear years after starting the drug. Recurrent abdominal pain with swelling episodes and a family history point towards hereditary angioedema, and a low C4 is a useful screening test.
- Ask about hives and itch; their absence points away from allergy.
- Check for an ACE inhibitor, even one started years ago.
- Send C4 and C1-inhibitor levels when recurrent angioedema has no clear trigger.
- Secure the airway early; bradykinin swelling will not settle with adrenaline.
- Stop the ACE inhibitor permanently after angioedema.
Why it matters
Treating bradykinin angioedema as allergy wastes the time in which the airway can still be secured calmly.
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