C4 Complement

Serum is the recommended specimen. Prior to centrifugation, allow the sample to clot 15-30 minutes at room temperature, then refrigerate 2-8⁰ C and allow clotting to continue for 30-60 minutes. To separate serum: rim the clot and centrifuge in refrigerated centrifuge. Serum should then be separated from the cells.

If cryoprecipitating antibodies are suspected, clot formation and centrifugation should proceed at 37⁰ C because complement fixation may occur if the specimen is chilled. In certain sera, chilling will significantly lower complement titer.

Serum Samples can be stored at 2 - 8⁰ C for up to 8 days and frozen <= -20⁰ C for up to 3 months without any loss of activity. Samples should be refrigerated or frozen if the assay cannot be run within 4 hours.

Complement testing may be ordered when a person has unexplained inflammation or edema or symptoms of an autoimmune disorder such as lupus. It may also be ordered when a healthcare 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.