Distinction between hereditary and acquired angioneurotic oedema according to the complement system

It is often impossible to make a clinical distinction between acquired and hereditary acute angioneurotic oedema. Investigation of the complement system is indispensable for this diagnosis to be established. The value of total complement and C4 and C2 are lowered in the sera in the hereditary form (44 cases) and normal in the acquired type (68 cases). The use of tests for the activation of C1 esterase "in vitro" is useful to distinguish these two types of oedema as has been demonstrated by the formal measurement of C1 esterase inhibitor.