Flow cytometry-based immunoassays for determining functional levels of plasma protease C1 inhibitor for the diagnosis of hereditary angioedema (HAE)

HAE types I and II are caused by a deficiency of functional C1 inhibitor (fC1-INH), leading to overproduction of bradykinin. Specific and sensitive methods to quantitate fC1-INH are required for accurate and timely diagnosis of HAE. Two commercially available assays either measure residual C1-esterase (C1s) activity or a complex ELISA measuring activated C1s. More physiologically relevant alternative methods measuring functional binding of Factor XIIa or kallikrein have been reported but they are not commercially available.