Complement: Measurement

Abstract

The complement system comprises a group of serum proteins and cell membrane receptors that function primarily to fight infection. Clinically, measurement of complement pathway activity and individual component levels is of value in (i) cases of suspected immunodeficiency with deficiencies of soluble components, including lectins, and of receptors leading to particular patterns of infection and (ii) conditions that involve complement activation such as systemic lupus erythematosis and renal translantion. This article describes functional and immunochemical methods that can be established in‐house or are available commercially. Until recently, measurement of complement in clinical situations has been aimed at identifying deficiency, of either level or function or activation. Mutations resulting in increased function have been identified for one component and this has opened a new area of research with clinical implications. Key Concepts: Correct sample collection and storage is essential for measurement of complement. Immunochemical measurement of circulating complement components can be performed by commercial assays, usually ELISA. Functional complement assays are required to detect deficiencies that do not affect immunochemical levels. Functional complement assays require buffers that are of the correct ionic strength and provide the requisite ions as well as being of the correct pH. Biosensor assays allow affinity and kinetic studies of complement component interaction.