Complement C3

There are nine major complement proteins. They are labeled C1 through C9. Complement proteins may be measured individually or together. A test called CH50 measures the overall activity of the whole complement system as a screen.

If the test shows that your complement protein levels are not normal or that the proteins aren't working with the immune system as well as they should, it can be a sign of an autoimmune disease or other health condition. If you have an autoimmune disease, your immune system attacks the healthy cells of your organs and tissues by mistake.

If your results show decreased levels or activity of complement proteins, it may mean that your body is using up complement faster than normal, which can happen with certain autoimmune diseases (such as lupus or rheumatoid arthritis), some kidney conditions (such as acute or chronic glomerulonephritis), hemolytic anemias, transplanted-organ rejection, certain blood-vessel infections, cryoglobulinemia, or with an inherited complement deficiency. Liver disease can also lead to lower levels because the liver makes many complement proteins.

If your results show increased levels or activity of complement proteins, it may mean that your body has acute or chronic inflammation. Higher activity has also been seen with certain cancers, such as leukemia, Hodgkin's disease, and sarcoma, and with Behcet's disease.

Talk with your provider about what your specific results mean for your health.