Section 866.5250 - Complement C[1] inhibitor (inactivator) immunological test system(a)Identification. A complement C1 inhibitor (inactivator) immunological test system is a device that consists of the reagents used to measure by immunochemical techniques the complement C1 inhibitor (a plasma protein) in serum. Complement C1 inhibitor occurs normally in plasma and blocks the action of the C1 component of complement (a group of serum proteins which destroy infectious agents). Measurement of complement C1 inhibitor aids in the diagnosis of hereditary angioneurotic edema (increased blood vessel permeability causing swelling of tissues) and a rare form of angioedema associated with lymphoma (lymph node cancer).(b)Classification. Class II (performance standards).