C3 / C4
Immune system proteins consumed during certain autoimmune flares.
What is it
Complement C3 and C4 are proteins of the immune system's complement cascade. Levels can be consumed (lowered) during active autoimmune disease.
Why it's measured
Low C3 and C4 have been associated with active lupus and certain other autoimmune conditions in published research.
Reference range
Standard laboratory reference
C3: 90 – 180 / C4: 10 – 40 mg/dL
Reference ranges vary by laboratory. Your individual reference range will appear on your test report and should be interpreted by your physician in the context of your overall health profile.
What results may indicate
Elevated
May reflect inflammation in research literature.
Lower
Has been associated with active autoimmune disease, particularly lupus flares.
These associations are general. They are not a personal diagnosis or prediction. Discuss your individual results with your physician in the context of your full health profile.
When it's measured
Used in evaluating autoimmune disease activity, especially lupus.
Related markers
Common questions
Complement C3 and C4 are proteins of the immune system's complement cascade. Levels can be consumed (lowered) during active autoimmune disease.
It's one of the markers used to build a fuller picture of your health. On its own it tells you very little, so it's most informative when reviewed alongside related markers.
It's measured from a standard blood draw at Quest or LabCorp. Complement C3 & C4 is one of the markers included in the OPTML Apex Panel, where your results are read across systems and reviewed by a U.S.-licensed physician.
Reference ranges vary by laboratory, and a single value rarely tells the whole story. Review your result with a physician in the context of your other markers, symptoms, and history.
Complement C3 & C4 is one signal among many. Answer a few quick questions and we’ll point you to the panel that fits.
Measured in
A complete look at your heart, hormones, metabolism, inflammation, and longevity systems — drawn at Quest or LabCorp, reviewed by a U.S.-licensed physician.
Find the right panel →This information is for general educational purposes only and is not medical advice. Lab results alone are not intended to diagnose, treat, or cure any condition and do not replace the advice of a healthcare provider. OPTML does not offer medical advice, a diagnosis, medical treatment, or any form of medical opinion.
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