Other
Complement C3
CONVERT & COMPARE
mg/dL
=
1.25
g/L
Reference ranges by source
Published adult intervals: 5, from 4 named sources, shown in mg/dL.
SOURCE
SEX
AGE
RANGE
VISUAL
CITE
Ages 0–17 (CALIPER)
3 age- and sex-stratified entries from the Canadian Laboratory Initiative on Pediatric Reference Intervals.
SOURCE
SEX
AGE
RANGE
VISUAL
CITE
About Complement C3
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 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.
Main source: MedlinePlus ↗
Useful for
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.
Diagnose or monitor rheumatoid arthritis, a condition that causes pain and swelling of the joints, often in the wrist, hands, and feet.
Help evaluate kidney conditions linked to immune system activity, such as certain forms of glomerulonephritis (inflammation of the kidney's filters).
Help diagnose certain bacterial, viral, or fungal infections.
Help look into inherited (genetic) complement deficiencies that can leave you more prone to infections.
Main source: MedlinePlus ↗
Interpretation
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.
For general wellness information only. Talk to a clinician about your specific results.
Main source: MedlinePlus ↗
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Related biomarkers
More tests in the other category.
Sources
A
ARUP Laboratories
M
Mayo Clinic Laboratories
L
Labcorp
Q
Quest Diagnostics
C
CALIPER: Canadian Pediatric Reference Intervals
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.