There was no difference in the levels of C3 or C3a between HAE-C1INH patients and controls, while C3d and iC3b were higher in patients compared to controls (p = 0.003 and p = 0.007, respectively), indicating a higher degree of complement activation involving the C3 convertase in HAE-C1INH patients. Here, C3 is linked to hereditary angioedema.