C4A and angioedema: Unlike in bradykinin-mediated angioedema, the levels and function of complement proteins (C4, C1q, C1 esterase inhibitor) are normal in histamine-mediated angioedema.1,2,12 Management involves airway preservation, epinephrine, steroids, and histamine H1/ H2 receptor blockers.1,2 In the ED setting, improvement of the angioedema in response to these treatments supports the diagnosis of histamine-mediated angioedema, even in cases without obvious urticaria or allergic manifestations.1,2