Angioedema differential & HAE pathway

Separates histaminergic (mast-cell) from bradykinin-mediated angioedema, routes ACE-inhibitor and hereditary angioedema, and links the C4 / C1-INH interpreter.

Evidence tier: Guideline-derived.

Decision points

  • Hives or pruritus with swelling?
  • On an ACE inhibitor?
  • C4 / C1-INH results?
  • Is C1q low?

Do-not-miss pitfalls

  • Do not mislabel bradykinin angioedema as allergic when it fails antihistamines/steroids.
  • Do not discharge tongue/laryngeal ACE-inhibitor angioedema without airway risk assessment.
  • Do not rely on a normal C4 alone when suspicion for HAE is very high, repeat and add C1-INH testing.
  • Do not order large food/aeroallergen panels for isolated angioedema without a compatible history.
  • HAE occurs without family history in ~25% of cases (de novo SERPING1 mutation), a negative family history does not exclude hereditary angioedema.
  • ARBs carry a small independent risk of angioedema (~0.1-0.7%); switching from an ACE inhibitor to an ARB removes most risk but does not eliminate it entirely, warn the patient.
  • Estrogen-containing medications (oral contraceptives, HRT) can trigger or worsen bradykinin-mediated angioedema including HAE, ask about estrogen use in all female patients with unexplained swelling.

Evidence & citations

  1. Maurer M, Magerl M, Betschel S, et al. The international WAO/EAACI guideline for the management of hereditary angioedema, 2021 revision and update. Allergy. 2022;77(7):1961-1990. PMID 35006617
  2. Zuberbier T, Abdul Latiff AH, Abuzakouk M, et al. The international EAACI/GA²LEN/EuroGuiDerm/APAAACI guideline for the definition, classification, diagnosis, and management of urticaria. Allergy. 2022;77(3):734-766. PMID 34536239
  3. Bernstein JA, Lang DM, Khan DA, et al. The diagnosis and management of acute and chronic urticaria: 2014 update. J Allergy Clin Immunol. 2014;133(5):1270-1277. PMID 24766875

Clinician decision support. Verify against the cited source. Not a substitute for clinical judgment. 100% on-device; no patient data is stored or transmitted.