Synonyms: C1; C1q; C2; C3; C4; CH50; CH100

 Why It Is Done

 Complement testing may be ordered when a person has unexplained inflammation or edema or symptoms of an autoimmune disorder such as SLE. It may also be ordered when a health practitioner suspects that someone may have an immune complex-related condition and wants to check the status of the person's complement system.

Individual complement components may be ordered when the total complement activity (CH50, sometimes called CH100) is abnormal to help determine which of the components are deficient or abnormal. C3 and C4 levels are the most frequently ordered, but others, such as C1 inhibitor, may be ordered when other deficiencies are suspected. C3 and C4 are often ordered together as the relative levels are often important.

When an acute or chronic condition has been diagnosed, complement testing may be used to help give a rough idea of the severity of the condition with the assumption that the severity is linked to the decrease in complement levels. Complement testing may also be ordered occasionally when a health practitioner wants to monitor the current activity of a condition.

How To Prepare

No special preparation is necessary