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Complement C3

Published: July 27, 2026Updated: August 25, 2026

Complement C3 is a blood protein that is part of the immune system's complement cascade, which plays a key role in defending against infections and in inflammatory responses.

Quick summary

Complement C3 is a biomarker for inflammatory and immune system activity.

Medically reviewed by WellAlly Editorial TeamLast reviewed August 25, 2026Editorial policy

Key facts at a glance

Units
mg/dL
Clinical utility
diagnostic
Result kind
quantitative
FDA-cleared
Roche C3, Abbott C3, Siemens C3
interpretation: {"text":"May indicate autoimmune disorders such as systemic lupus erythematosus (SLE), or certain types of kidney disease.","label":"Low"}; {"text":"Suggests acute or chronic inflammation, infections, or other inflammatory conditions.","label":"High"}

Complement C3 is a critical component of the complement system, a part of the immune system that enhances the ability of antibodies and phagocytic cells to clear pathogens and damaged cells from the body.

Levels of Complement C3 can be measured in the blood to assess the activity of the complement system, which is often elevated in inflammatory conditions and infections.

Abnormal levels of Complement C3, either too high or too low, can indicate various medical conditions, including autoimmune disorders, infections, and liver disease.

Frequently asked questions

What is the normal range for Complement C3?
The normal range for Complement C3 is typically between 75–175 mg/dL.
What conditions can cause low Complement C3 levels?
Low levels of Complement C3 can be caused by autoimmune disorders, such as lupus, or certain types of kidney diseases.
  1. 1
    Complement C3 - Lab Tests OnlineSource
  2. 2
    Mayo Clinic - Complement C3Source

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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 25, 2026. · Read our editorial policy