Complement (C3 & C4)
Immunology and Allergy Overview / Directory
Purpose of the test
The complement system is a complex series of some 30 proteins, two-thirds of which circulate in the plasma while the remainder are present on cell and tissue surfaces. Complement components are rapidly synthesised and released into the circulation following trauma or inflammation and elevated concentrations are common in many acute illnesses. Complement consumption can also take place in certain disease states, and complement concentration can be useful in diagnosis and monitoring progress. When present, low concentrations indicate increased consumption or decreased synthesis.
C3 and C4 concentrations should be requested in patients with renal disease, joint disease, 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 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.
Reference Range
The normal ranges of C3 and C4 do not alter with age.
C3 0.65 - 1.65 g/L;
C4 0.16 – 0.60 g/L
Sample Requirements
Serum is preferred, as is measurement on day of venepuncture. EDTA plasma is acceptable. All samples must show no signs of deterioration and lipaemic samples should be avoided.
Storage and Transport
Samples may be stored at 4°C prior to analysis
Turnaround Time
1 working day
Time Limit for Extra Tests
Five days
Factors affecting results or interpretation
All tests are compromised by prolonged transit times. For this reason, date of bleed and date of postage must be provided with each request.
Price
Price available on application - please contact adrianturner1@nhs.net. Discounts could be available for significant workloads.
Contacts
John Cazabon or Rosemary Ebling, Lead Biomedical Scientists
T 020 3299 1559
