Normal Reference Ranges
Adult
15 - 45 mg/dL
Pediatric
15 - 45 mg/dL
Clinical Significance
Component of the classical complement pathway. Often measured with C3. Very low in hereditary angioedema and active Lupus.
Causes of High
- Acute phase reaction (inflammation)
- Malignancy
Causes of Low
- Systemic Lupus Erythematosus (SLE)
- Cryoglobulinemia
- Hereditary Angioedema (C1 esterase inhibitor deficiency)