Complement C3

What it measures

Measures C3, the central protein of the complement system. It is used to assess immune-complex diseases such as SLE and certain glomerulonephritides.

Specimen and preparation

• Specimen: Serum
• Tube: Gold top
• Preparation: Separate promptly; complement is labile at room temperature.

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-phase response: infection, inflammation, pregnancy
• Obstructive jaundice
• Some tumours

Causes of low values

• Active SLE, especially lupus nephritis
• Post-streptococcal and membranoproliferative glomerulonephritis
• C3 glomerulopathy
• Sepsis and severe liver disease

Method

Immunoturbidimetry or nephelometry

Good to know

Low C3 with normal C4 suggests alternative pathway activation (e.g. post-infectious GN).

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