The Complement Component C4 (C4 test) measures the levels of C4 protein in the blood, which is part of the complement system—a crucial component of the immune system. This test helps diagnose immune system disorders, autoimmune diseases, and complement deficiencies.
🔹 Diagnosing Autoimmune Diseases – Lupus (SLE), Rheumatoid Arthritis (RA), Vasculitis
🔹 Evaluating Complement Deficiencies – Hereditary Angioedema (HAE), Recurrent Infections
🔹 Assessing Chronic Inflammatory Conditions – Kidney diseases, Liver diseases
🔹 Monitoring Disease Activity – Helps track disease progression and response to treatment
Adults: 10-40 mg/dL (varies slightly by lab)
Children: Similar to adult range
| C4 Level | Possible Causes |
|---|---|
| Low C4 | – Systemic Lupus Erythematosus (SLE) 🦋 (especially active lupus nephritis) – Hereditary Angioedema (HAE) 😷 – Liver Disease (e.g., Cirrhosis, Hepatitis) – Immune Complex Diseases (e.g., Glomerulonephritis, Vasculitis) – Complement Deficiency (Genetic or Acquired) |
| High C4 | – Acute Inflammation or Infection – Certain Cancers (e.g., Lymphoma) – Autoimmune Hemolytic Anemia |
🔹 Complement C3 Test – Often tested alongside C4 to assess immune function
🔹 CH50 (Total Complement Activity Test) – Evaluates overall complement system activity
🔹 ANA (Antinuclear Antibody Test) – Helps diagnose autoimmune diseases like Lupus
✅ Further autoimmune testing (e.g., ANA, Anti-dsDNA for lupus)
✅ Liver function tests if liver disease is suspected
✅ Genetic testing for Hereditary Angioedema (HAE) if symptoms match
✅ Regular follow-ups to monitor disease progression