Section 866.5260 - Complement C[3b] inactivator immunological test system(a)Identification. A complement C3b inactivator immunological test system is a device that consists of the reagents used to measure by immunochemical techniques the complement C3b inactivator (a plasma protein) in serum. Complement is a group of serum proteins that destroy infectious agents. Measurement of complement C3b inactivator aids in the diagnosis of inherited antibody dysfunction.(b)Classification. Class II (performance standards).