The C4 Complement Test assesses the amount of Complement 4 (C4) in the blood. C4 is part of the complement system, a crucial component of the immune system that enhances the ability of antibodies and white blood cells to fight infections and remove damaged cells. Low or high C4 levels may indicate autoimmune diseases, chronic infections, or immune deficiencies.
Why is the C4 Complement Test Done?
✔ To diagnose and monitor autoimmune diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and Sjögren’s syndrome.
✔ To assess immune system function in patients with frequent infections.
✔ To evaluate inflammation levels in the body.
✔ To check for hereditary complement deficiencies, which can increase susceptibility to infections.
Who Should Get This Test?
📌 People with suspected autoimmune diseases, experiencing:
- Chronic fatigue and joint pain.
- Skin rashes, including the butterfly rash (common in lupus).
- Persistent infections or inflammation.
📌 Patients with unexplained inflammation, swelling, or recurrent infections.
📌 Individuals with a family history of complement system disorders.
How is the C4 Complement Test Performed?
Preparation:
- No fasting or special preparation required.
- Avoiding certain medications may be advised by your doctor.
Procedure:
- A blood sample is drawn from a vein in the arm.
- The sample is analyzed using Nephelometry, which detects protein concentrations.
- Results are usually available within 24-48 hours.
Understanding the Results
| C4 Levels | Possible Indications |
|---|---|
| Normal Range | 10-40 mg/dL |
| Low C4 Levels | Systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), chronic infections, complement deficiencies |
| High C4 Levels | Acute or chronic inflammation, certain infections, cancer |
⚠ Low C4 levels, especially with low C3, are strong indicators of lupus and other autoimmune conditions.
Conditions Associated with Abnormal C4 Levels
📌 Low C4 Levels:
- Systemic Lupus Erythematosus (SLE) – C4 is consumed in immune system overactivity.
- Rheumatoid Arthritis (RA) – Chronic inflammation reduces complement levels.
- Chronic infections – Conditions like tuberculosis or bacterial sepsis.
- Hereditary complement deficiencies – Genetic disorders causing immune dysfunction.
📌 High C4 Levels:
- Acute inflammation from infections, trauma, or injury.
- Certain cancers, including lymphoma and leukemia.
- Liver diseases – Conditions affecting complement protein production.
Limitations of the Test
❌ Cannot diagnose a specific disease alone; other tests like C3 Complement Test and ANA test may be needed.
❌ Medications like corticosteroids may alter results.
❌ C4 levels fluctuate with disease activity, requiring periodic testing for monitoring.
Why is the C4 Complement Test Important?
✔ Essential for diagnosing and monitoring autoimmune diseases.
✔ Helps assess immune function and inflammatory status.
✔ Guides treatment strategies in immune-related conditions.
The C4 Complement Test is a valuable diagnostic tool for autoimmune diseases, chronic infections, and immune deficiencies, helping doctors tailor appropriate treatments and improve patient outcomes.
