Blood
Complement CH50
Also known as: Total Complement, CH50
About Complement CH50
A complement blood test measures the levels and/or activity of a group of proteins that are part of the complement system. This system "complements" or enhances your body's defenses against infections and other diseases. Your immune system makes antibodies, which are proteins to fight disease-causing substances like viruses and bacteria. The proteins in the complement system will also help fight the infection or disease. These proteins work together in a sequence, with one protein activating the next.
There are nine major complement proteins. They are labeled C1 through C9. Complement proteins may be measured individually or together. A total complement test, also called CH50 or CH100, is a screening test that looks at the overall amount and activity of all the complement proteins in your blood working together.
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.
Main source: MedlinePlus ↗
Useful for
Screen for a problem with the complement system as a whole, since CH50 reflects how all the complement proteins are working together.
Help diagnose or monitor autoimmune diseases such as lupus, a chronic (long-lasting) disease that affects many parts of the body, including the joints, blood vessels, kidneys, and brain.
Help evaluate rheumatoid arthritis, a condition that causes pain and swelling of the joints, often in the wrist, hands, and feet.
Help diagnose certain bacterial, viral, or fungal infections.
Main source: MedlinePlus ↗
Interpretation
If your results show decreased levels or activity of complement proteins, it may mean that your body is trying to get rid of foreign substances or attacking its own tissues.
Decreased levels may be a sign of conditions such as autoimmune diseases (including lupus and rheumatoid arthritis), inherited complement deficiencies, recurrent bacterial infections, kidney disease (such as some types of glomerulonephritis), liver disease, malnutrition, certain blood disorders (such as some hemolytic anemias and cryoglobulinemia), an organ transplant rejection, an infection of the heart valves (subacute bacterial endocarditis), or cirrhosis.
If your results show increased levels or activity of complement proteins, it may mean that your body has acute or chronic inflammation.
Increased levels may be a sign of conditions such as cancer (including leukemia, Hodgkin's disease, and certain sarcomas), ulcerative colitis, Behcet's disease, or other inflammatory conditions.
For general wellness information only. Talk to a clinician about your specific results.
Main source: MedlinePlus ↗
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Sources
Last updated 2026-05-02
This page presents source-specific reference data and sourced explanations. For general wellness information only. This is not medical advice. For diagnosis or treatment of any condition, talk to a qualified clinician.