Imperial Collage Healthcare

Complement C3 and C4 components


Test Background
Lowered C3 or C4 levels may be due to excessive consumption of the complement cascade, as seen in immune complex-mediated disease, such as SLE with associated renal disease, or cryoglobulinaemic nephritis. May indicate disease flare or aid prognosis. Also, components can be low due to genetic/acquired defects. Commonest cause of low C3 and C4 is sample degradation. Raised levels may indicate an acute phase response.


Clinical Indications

  • Diagnosis of glomerulonephritis
  • Diagnosis of HAE or cryoglobulinaemia
  • Diagnosis or exclusion: acute phase increases vs. underlying paraprotein pathology (serum electrophoresis reflex testing)
  • Some utility in monitoring autoimmune conditions, such as SLE
  • Single point determinations of C3 and C4 are of limited value and serial measurements are recommended.


Reference Range

C3 : 0.7-1.7 g/L
C4 : 0.16-0.54 g/L


Sample Required
SST (gold top)


Sample Volume
5-10 mL (1 mL serum)


Turnaround Time
4 days


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