Serum or plasma mass concentration of a specific protein (e.g., complement component C3)
This test measures the amount of a protein called C3 in your blood. C3 is part of your immune system and helps fight infections.
["C3 helps your body defend against bacteria and viruses."]
Key facts at a glance
- LOINC
- 21035-1
- Short code
- 11DC AM SerPl-mCnc
- Synonyms
- 11DC AM SerPl-mCnc
- Category
- hormone
- 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 Does This Test Measure?
C3 is a key protein in your immune system’s complement pathway. It plays a role in identifying and marking pathogens for destruction by other immune cells. Low levels may suggest immune system issues, while high levels could indicate certain inflammatory conditions or autoimmune responses.
Why Might You Need This Test?
Your healthcare provider may order this test if you have symptoms like frequent infections, joint pain, or signs of an overactive immune response. It’s also used to monitor conditions like lupus, kidney disease, or infections.
Common Reasons for Testing
Tests like this are often done when diagnosing or managing conditions affecting the immune system, kidney function, or inflammation. It may also be part of routine monitoring for patients with chronic illnesses.
What to Expect Before the Test
No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if it involves drawing blood from your arm. Tell your provider about any medications or supplements you’re taking, as they may affect results.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
◆Associated findings1
Short name
C3 Protein Level
Frequently asked questions
Your results will be compared to a general reference range for healthy adults. While exact values vary by lab, low C3 levels may signal immune dysfunction, while very high levels could indicate inflammation or other conditions.
A low C3 level may suggest weakened immune function, chronic infections, or certain autoimmune diseases. Your doctor will consider your symptoms and other test results to determine the cause and next steps.
High C3 levels can occur with infections, inflammation, or some autoimmune conditions. It’s important to discuss these results with your provider, as they may guide further testing or treatment plans.
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