Serum/plasma concentration of complement component C3 (substance concentration)
This test measures the amount of C3, a key protein in your immune system’s complement system, which helps fight infections and control inflammation. Low levels may indicate immune system issues or certain medical conditions.
["Your immune response and inflammation may need attention if your C3 levels are outside expected ranges."]
Key facts at a glance
- LOINC
- 1003-3
- Short code
- IAT Comp-Sp Reag SerPl Ql
- Synonyms
- IAT Comp-Sp Reag SerPl Ql
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What Is C3?
C3 is part of the complement system—a network of proteins that enhance your immune response. It helps identify and destroy pathogens (like bacteria and viruses) and signals other immune cells to clear debris. It also plays a role in regulating inflammation.
Why Is It Tested?
Doctors may order this test if you have symptoms of immune disorders (e.g., frequent infections), kidney disease, or autoimmune conditions. It can also help monitor treatments for conditions like lupus or certain infections.
What Could Affect Results?
Several factors may influence C3 levels, including chronic illnesses, infections, medications (like steroids), or recent vaccinations. Blood collection timing (e.g., fasting) and specimen handling can also impact results.
Common Reasons for Testing
Common reasons include diagnosing or managing immune-related conditions (e.g., lupus, chronic infections), evaluating kidney function, or assessing response to treatments like chemotherapy or immunosuppressants.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Low C3 levels may suggest immune dysfunction, such as chronic infections, autoimmune diseases (e.g., lupus), or kidney problems. Very low levels could indicate severe immune suppression. High levels might rarely be seen in certain genetic disorders or overactive immune responses, but this is less common. Always discuss results with your healthcare provider.
Short name
C3 Protein Level
Frequently asked questions
What does a low C3 level mean?
What if my C3 level is high?
How soon will I get my results?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
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 16, 2026. · Read our editorial policy