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Immunology Laboratory

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Complement Levels

Also known as: C3; C4; Comp

Measurement of serum complement levels are useful in patients with renal disease, connective tissue diseases, and multi-system disorders with evidence of vasculitis.

A low complement concentration would suggest an immunological basis for the symptoms. C3 and C4 concentrations are often low in patients with active SLE. Low C3 and normal C4 concentrations are seen in patients with Gram negative septicaemia and some forms of glomerulonephritis. Low C4 is also seen in cryoglobulinaemia.

Complement concentrations should also be measured in patients with recurrent infections, with normal or raised immunoglobulin concentration.

Specimen requirements

Serum 1ml


Price on application

Laboratory turnaround time

3 days

Laboratory method


Assay interferences

Microbially contaminated, heat-treated samples should not be used.

Grossly haemolysed, icteric or lipaemic specimens should be avoided. EDTA plasma samples are contraindicated for the analysis of C3 and C4 as increased fibrinogen levels may artificially give depressed results.

Reference range/units

  • C3 65 - 190 mg/dl
  • C4 14 - 40 mg/dl

Associated tests

Not applicable

Sample stability


4 days at 2-8ºC


1 week at 2-8ºC

Shipping and storage

UK and Ireland

Ambient temperature and first class post. Hays DX users please enquire via email below.


Ambient temperature if courier will deliver within 72 hours otherwise consider refrigerated transport. Freezing is not a requirement.

Ensure delivery Monday to Friday 09:00 - 17:30.

Further information and contact details

For further information, email

Last reviewed:06 October 2023