Complement 4 (C4) Level, Serum
Complement 4 (C4) Level Test
The Complement 4 (C4) Level, Serum test measures the amount of Complement C4 protein in the blood. C4 is part of the complement system, a group of proteins that support the immune system in fighting infections, clearing damaged cells, and regulating inflammation. This test is commonly used to evaluate autoimmune disorders, inflammatory conditions, and immune system activity.
Why is this test done?
Doctors may recommend a C4 Level test to:
- Diagnose and monitor autoimmune diseases such as lupus or rheumatoid arthritis
- Evaluate recurrent infections or immune deficiencies
- Assess inflammatory disorders
- Monitor hereditary angioedema
- Investigate kidney diseases related to immune disorders
Symptoms that may require testing
- Joint pain or swelling
- Persistent fatigue
- Skin rashes
- Recurrent infections
- Unexplained inflammation
- Swelling episodes (angioedema)
Sample Required
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Sample Type: Serum
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Preparation: Usually no fasting required unless advised by your doctor
Normal Reference Range
Reference values may vary slightly between laboratories, but typical serum C4 levels are:
Understanding the Results
Low C4 Levels may indicate:
- Systemic Lupus Erythematosus (SLE)
- Autoimmune diseases
- Chronic liver disease
- Hereditary angioedema
- Certain kidney disorders
High C4 Levels may indicate:
- Acute inflammation
- Certain infections
- Metabolic disorders
- Some cancers
Benefits of the Test
- Helps detect immune system abnormalities
- Assists in diagnosing autoimmune diseases
- Useful for monitoring disease activity and treatment response
- Supports early medical intervention
