C4A Protein (Factor Xa Inhibitor) in Plasma
This test measures the amount of C4A protein, a complement system component that helps regulate immune responses. It may be checked if you have symptoms of immune-related conditions or after certain treatments.
["C4A protein helps control inflammation and immune reactions; levels may be checked for suspected immune disorders or after immune-modifying therapies."]
Key facts at a glance
- LOINC
- 4501-3
- Short code
- C4A
- Synonyms
- C4a Plas-mCnc
- Category
- chemistry
- Sample
- plasma
- Container
- EDTA plasma tube (lavender-top); plasma separator tube (PST) also acceptable
- Units
- N/A
- Ref low
- 100
- Ref high
- 400
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- Enzyme-Linked Immunosorbent Assay (ELISA)
- CPT
- 86161
- SNOMED
- 31968009
- Specimen volume
- 1.0 mL plasma
- Stability
- Ambient: 2 hours; Refrigerated (2-8°C): 24 hours; Frozen (-20°C or below): up to 6 months. Avoid repeated freeze-thaw cycles.
- Hemolysis max
- 100
- Lipemia max
- 100
- Icterus max
- 50
- TAT
- 24–72 hours
- Order
- routine
Why This Test Might Be Ordered
Your healthcare provider may recommend this test if you have symptoms like chronic inflammation, autoimmune conditions (such as lupus or rheumatoid arthritis), or after receiving immune-suppressing treatments. It may also be used to monitor certain genetic disorders or complement system abnormalities.
What to Expect Before the Test
No special preparation is needed. You’ll provide a blood sample drawn from a vein, typically in a clinic or lab. The sample is processed into plasma for testing.
How the Test Works
The test measures the concentration of C4A protein in your plasma using a specialized immunoassay method. This helps assess its role in immune function and inflammation.
Possible Results and Interpretation
Results are compared to a reference range specific to your age, sex, and health status. Low levels may suggest immune dysfunction or certain genetic conditions, while high levels could indicate overactive immune responses or other underlying issues.
Reference range
Typically 100-400 ng/mL or 0.10-0.40 mg/L in healthy adults; reference ranges vary by laboratory and assay methodology. Consult your laboratory's specific reference interval.N/A
No special patient preparation required. Fasting is not necessary.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Low C4A protein levels may be linked to inherited complement deficiencies, autoimmune diseases, or immune suppression. High levels could signal chronic inflammation, infections, or other immune-related conditions. Your provider will discuss these findings in the context of your symptoms and medical history.
Short name
C4A Protein Level
Frequently asked questions
What causes low C4A protein levels?
What causes high C4A protein levels?
Can diet or lifestyle affect C4A protein levels?
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 14, 2026. · Read our editorial policy