Complement 4 (C4)
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C4 plays a crucial role in autoimmune surveillance, inflammation, and immune regulation
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🧬 Complement 4 (C4) Test
Parameter | Complement Component 4 (C4) |
|---|---|
Sample Type | Serum (via blood sample) |
Fasting Required | ❌ Not required |
Normal Range | 10–40 mg/dL (may vary slightly by lab) |
Department | Immunology / Rheumatology / Nephrology |
Turnaround Time | 1–2 working days |
🔍 What is Complement C4?
- C4 is a key protein in the classical complement pathway, part of the innate immune system.
- It works with C1 and C2 to help fight infections and clear immune complexes.
- C4 plays a crucial role in autoimmune surveillance, inflammation, and immune regulation.
🧭 Why Is the C4 Test Done?
Clinical Purpose | Used To |
|---|---|
Diagnose or monitor Systemic Lupus Erythematosus (SLE) | C4 is consumed during flares, especially with kidney involvement |
Evaluate hereditary angioedema (HAE) | Low C4 is a key diagnostic clue |
Investigate immune complex diseases | Like glomerulonephritis, vasculitis, cryoglobulinemia |
Check for complement deficiencies | In patients with recurrent infections |
Monitor autoimmune or inflammatory diseases | Track disease activity |
📉 Low C4 Levels May Indicate
Condition | Explanation |
|---|---|
Active Lupus (SLE) | C4 is used up in immune complex activation |
Hereditary Angioedema (HAE) | Due to C1 esterase inhibitor deficiency leading to C4 depletion |
Post-infectious glomerulonephritis | Complement consumption due to immune activation |
Mixed cryoglobulinemia | Associated with C4 consumption |
Complement deficiency (genetic) | Rare cause of recurrent bacterial infections |
📈 High C4 Levels May Indicate
Condition | Explanation |
|---|---|
Acute inflammation | C4 is a mild acute-phase reactant |
Chronic infections or cancer | Occasionally raised in inflammatory states |
Obesity or metabolic syndrome | Mild elevation alongside other markers like CRP |
🔬 Commonly Ordered With
Test | Purpose |
|---|---|
C3 Complement | Assess the entire complement cascade (C3 + C4) |
C1 Esterase Inhibitor Level & Function | To confirm hereditary angioedema |
ANA (Antinuclear Antibodies) | Autoimmune disease screening |
Anti-dsDNA, Anti-Smith | Lupus-specific markers |
CRP / ESR | General inflammatory markers |
Urine Protein / Creatinine Ratio | To monitor lupus nephritis |
📝 Summary Table
Aspect | Complement C4 Test |
|---|---|
Biological Role | Part of the classical pathway of the complement system |
Low in | Lupus, hereditary angioedema, immune complex diseases |
High in | Acute or chronic inflammation, metabolic conditions |
Clinical Uses | Autoimmune screening, nephritis monitoring, HAE diagnosis |
Next Steps if Abnormal | C3, C1-INH, ANA, dsDNA, CRP, urine protein tests |
How our test process works!
