Figure 1From: Hereditary angioedema: New therapeutic options for a potentially deadly disorder HAE differential diagnostic algorithm. C4 complement protein levels can be used as a screening test for HAE. Low C1 inhibitor levels support an HAE diagnosis in the absence of a family history since 25% of HAE cases are the result of spontaneous mutations in individuals. Reproduced with permission from Zingale et al.[35]Back to article page