Hereditary C1 inhibitor deficiency is associated with high spontaneous amidase activity

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Angioedema diagnosis classically targets the complement system (via C1 inhibitor (C1Inh) function and antigenic C4 level) and contact phase activation (via amidase activity). Bradykinin is responsible for angioedema attacks and is produced from contact phase activation secondary to failed C1Inh control.


We aimed to compare the diagnostic performances of spontaneous amidase activity and antigenic C4 level in C1Inh hereditary angioedema (C1Inh-HAE) patients.


Samples from 185 C1Inh-HAE patients (81 men, 104 women; confirmed by SERPING1 gene mutations) and from 99 blood donors (50 men, 49 women) were tested for C1Inh function, antigenic C4 level and spontaneous amidase activity.


In the C1Inh-HAE group, antigenic C4 level was decreased (n = 135) and amidase activity was increased (n = 181). Receiver operating characteristic analyses showed higher diagnostic performance values for the spontaneous amidase assay compared to those of antigenic C4.


The spontaneous amidase activity assay should replace antigenic C4 level testing and should be tested alongside the C1Inh function for both AE screening and follow up of HAE patients.

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