COL18A1 and hereditary angioedema: However, in case of a high suspicion of HAE with normal C1-inhibitor, assessment for known mutations underlying HAE-nC1-INH is recommended.8While C1-inhibitor level and function remain the golden standard for diagnosis of HAE type 1 and 2, analysis can take weeks, making them impractical to distinguish HAE from other forms of angioedema in the acute setting.