A complement test is a blood test that measures the activity of a group of proteins in the bloodstream. These proteins make up the complement system, which is one part of the immune system.
A common use for a complement test is to diagnose autoimmune diseases or other immune function conditions. A doctor can use a complement test to monitor the progress of a person undergoing treatment for an autoimmune disease such as systemic lupus (SLE) or rheumatoid arthritis (RA).
Normal Values for C3: 75 to 175 mg/dL
Normal Values for C4: 14 to 40 mg/dL
