Use

The C1 esterase inhibitor protein functions as a serine protease inhibitor (serpin) within serum, inhibiting complement proteases such as C1r, C1s, as well as kallikrein and factors XIa, XIIa and plasmin. Concentrations of this protein are reduced to approximately 10–30% of normal in patients with hereditary angioedema (HAE), which accounts for around 85% of HAE cases. In about 15% of HAE patients, protein concentration remains normal but functional activity is reduced. Measurement of C1 esterase inhibitor protein concentration aids in the diagnosis of HAE and in differentiating between types I and II disease. (citing Quest Diagnostics Nichols Institute details and FAQs)