The Complement C3 test measures the level of C3 protein in the blood. C3 is a key component of the complement system, which helps the immune system fight infections, remove pathogens, and regulate inflammation.
🔹 Autoimmune Disease Diagnosis – Helps diagnose Systemic Lupus Erythematosus (SLE), Rheumatoid Arthritis (RA)
🔹 Chronic Infections – Low C3 may indicate recurrent bacterial infections
🔹 Kidney Diseases – Glomerulonephritis (GN), Membranoproliferative GN
🔹 Complement System Deficiency – Identifies genetic or acquired complement deficiencies
🔹 Monitoring Disease Activity – Tracks progression of lupus or immune complex diseases
Adults & Children: 75-175 mg/dL (varies slightly by lab)
| C3 Level | Possible Causes |
|---|---|
| Low C3 | – Systemic Lupus Erythematosus (SLE) (especially lupus nephritis) 🦋 – Glomerulonephritis (GN) (Post-streptococcal GN, MPGN) – Sepsis or Chronic Infections – Complement Deficiencies (Inherited disorders) |
| High C3 | – Acute or Chronic Infections (Bacterial, Viral) – Chronic Inflammatory Diseases – Obesity, Metabolic Syndrome – Certain Autoimmune Disorders |
🔹 Complement C4 Test – Often tested with C3 to evaluate immune function
🔹 CH50 Test (Total Complement Activity) – Assesses overall complement system activity
🔹 ANA (Antinuclear Antibody Test) – Helps diagnose autoimmune diseases like Lupus
🔹 Kidney Function Tests – If kidney disease is suspected (e.g., Creatinine, Urinalysis)
✅ Further testing for autoimmune diseases (e.g., ANA, Anti-dsDNA for lupus)
✅ Kidney function tests if glomerulonephritis is suspected
✅ Infection screening if C3 is low due to bacterial infections
✅ Regular monitoring for disease progression and treatment response