In the C1‐INH‐HAE type II, C4 levels were low but C1‐INH concentrations were elevated or normal, accompanied by low fC1‐INH, in which case, if the above results were seen, we determined the level of C1q, which is typically normal in the hereditary form and low in the acquired form of C1‐INH deficiency (C1‐INH‐AAE). Here, SERPING1 is linked to acquired angioedema.