Complement C4

What it measures

Measures C4, part of the classical and lectin complement pathways. Low levels point to classical pathway consumption or inherited deficiency.

Specimen and preparation

• Specimen: Serum
• Tube: Gold top
• Preparation: Separate promptly; avoid delays.

Reference range

Reference ranges differ between laboratories, methods and populations. Always use the range printed on your own lab report.

Causes of high values

• Acute inflammation
• Pregnancy
• Some tumours

Causes of low values

• Active SLE
• Cryoglobulinemia (hepatitis C)
• Hereditary angioedema (C1-inhibitor deficiency)
• Inherited C4 deficiency

Method

Immunoturbidimetry or nephelometry

Good to know

Very low C4 between attacks of swelling is a useful screen for hereditary angioedema.

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