Detection of complement in relation to disease

If a single component is lowered, it is reasonable to question whether the patient has a genetically-controlled defect. Studies of family members may be required. If split products, complexes, or neoantigens are present, it is likely that there is ongoing complement activation. If most of the components of a pathway are lowered, a reasonable supposition is that complement is being activated. We then turn to a consideration of the factors that may activate complement. When hypocomplementemia is associated with a decrease in titer of several components, it is often possible to determine whether the classic or alternative pathway is the major pathway being activated; this, in turn, may suggest certain diagnoses and rule out other diagnoses. The nature of the circulating complexes or split products may provide the same information. Thus, a consideration of the pathophysiology of the complement system and of the factors that activate complement provides an approach to an understanding of the function of complement and the role of complement causing a damage in a clinical setting.