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Complement C4 Normal Ranges
C4 (Complement component 4) is an early-pathway complement protein involved in immune complex clearance.
| Age Group | Reference Range | Unit | Notes |
|---|---|---|---|
| Adults (18–64) | 16 – 47 | mg/dL | — |
Also reported in: g/L.
Common Causes of High C4
Acute phase response (C4 is a mild acute phase reactant)
Common Causes of Low C4
Active SLE / lupus nephritis (most common clinical cause — immune complex consumption)Hereditary angioedema types 1 and 2 (C1-inhibitor deficiency — C4 is low even between attacks)C4 null alleles (genetic — no disease, just constitutional low C4)
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