Complement Blood Test Test
A complement blood test measures the levels and activity of proteins in your complement system, which helps your immune system fight infections. Abnormal results can indicate autoimmune diseases, infections, or other health conditions.
What this test measures
A complement blood test measures the levels and/or activity of a group of proteins that are part of the complement system. These proteins work together to help your immune system fight infections and diseases. The test may measure individual proteins like C3 and C4, or total complement activity (CH50 or CH100).
What your results mean
Reference ranges vary by laboratory and by your age and sex. MedlinePlus does not publish a single normal range for this test — always read your result against the range printed on your own lab report and discuss it with your provider.
Higher-than-normal results
Increased levels or activity of complement proteins may mean your body has acute or chronic inflammation. This could be a sign of certain cancers (like leukemia or non-Hodgkin lymphoma) or ulcerative colitis. If you are being treated for lupus or another autoimmune disease, increased levels may mean your treatment is working.
Lower-than-normal results
Decreased levels or activity of complement proteins may mean your body is trying to get rid of foreign substances or attacking its own tissues. This could be a sign of lupus, rheumatoid arthritis, cirrhosis, certain kidney diseases, hereditary angioedema, malnutrition, or a recurring infection.
Frequently asked questions
What is a complement blood test used for?
It is most often used to diagnose or monitor autoimmune diseases such as lupus and rheumatoid arthritis. It may also help diagnose certain bacterial, viral, or fungal infections.
What are the nine major complement proteins?
They are labeled C1 through C9. C3 and C4 are the most commonly tested individual complement proteins.
What does a CH50 test measure?
A CH50 test (sometimes called CH100 or total complement test) measures the total activity and levels of all the major complement proteins.
What does a low complement level mean?
Low levels may indicate lupus, rheumatoid arthritis, cirrhosis, certain kidney diseases, hereditary angioedema, malnutrition, or a recurring infection.
What does a high complement level mean?
High levels may indicate acute or chronic inflammation, certain cancers (like leukemia or non-Hodgkin lymphoma), or ulcerative colitis. In people being treated for lupus, high levels may mean treatment is working.
Related lab tests
Sources
- MedlinePlus: Complement Blood Test — NIH MedlinePlus
Last updated . Information is aggregated from official public sources and is not a substitute for professional medical care.