Serum or plasma concentration of complement component C3
This test measures the level of C3, a key protein in your immune system’s complement pathway, which helps fight infections and regulate inflammation.
["C3 helps protect your body by identifying and removing harmful substances, like bacteria or damaged cells."]
Key facts at a glance
- LOINC
- 38388-5
- Short code
- C3
- Synonyms
- C3 SerPl Ql
- Category
- chemistry
- Sample
- serum
- Container
- Serum separator tube (SST) or red-top tube
- Units
- N/A
- Ref low
- 90
- Ref high
- 180
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Immunonephelometry
- CPT
- 86160
- SNOMED
- 166037005
- Specimen volume
- 1 mL serum
- Stability
- Stable for 8 hours at room temperature, 7 days at 2-8°C, or 2 months at -20°C
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What Is C3 Used For?
C3 levels can help diagnose or monitor conditions affecting your immune system, such as infections, autoimmune diseases, or kidney problems. It may also be checked after certain treatments or surgeries to assess immune function.
When Might You Need This Test?
Your doctor may order this test if you have symptoms like frequent infections, unexplained fatigue, swelling, or signs of an immune or inflammatory condition. It’s also sometimes checked during routine evaluations or before certain medical procedures.
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’s drawn from your blood. Avoid strenuous activity or smoking on the day of the test.
What Happens During the Test?
A healthcare provider will draw blood from a vein in your arm. You may feel a slight pinch, but it’s quick and typically not painful. The blood sample is then sent to a lab for analysis.
Reference range
Adults: 90-180 mg/dLN/A
No special patient preparation required. Fasting is not necessary.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Low C3 levels may indicate immune system dysfunction, infections, or conditions like lupus, kidney disease, or liver problems. High levels could suggest chronic inflammation or certain immune disorders. Your doctor will interpret results in the context of your symptoms and medical history.
Short name
C3 Serum/Plasma Level
Frequently asked questions
Why might my C3 level be checked regularly?
Could my diet affect my C3 levels?
What if my C3 level is outside the expected range?
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