C3 Complement

The C3 Complement blood test measures Complement Component 3, commonly abbreviated to C3, one of the central proteins within the complement immune system.

The complement system is made up of multiple proteins that work together to recognise pathogens, support antibody function, clear immune complexes and contribute to inflammation.

C3 occupies a particularly important position because the classical, lectin and alternative complement pathways all converge on activation of C3.

The test contains 1 biomarker: C3 Complement.

Reduced C3 concentrations can occur when complement is being consumed during active immune processes. Examples include systemic lupus erythematosus, some immune-complex diseases, severe infections and selected forms of glomerulonephritis.

The pattern of C3 relative to C4 can provide additional information. Low C3 with a relatively normal C4 may suggest activation of the alternative pathway, whereas reduction of both C3 and C4 can occur with classical-pathway activation in immune-complex disease.

C3 is also an acute-phase protein, meaning concentrations may increase during inflammation or infection.

For this reason, a normal or elevated C3 result does not automatically mean that complement activity is normal.

C3 should be interpreted alongside C4, symptoms, clinical history, kidney findings and other immunology investigations where appropriate.

The expected turnaround time for the C3 Complement test is approximately 1 business day after your sample arrives at the laboratory.

Results are sent securely by email once laboratory analysis and authorisation are complete.

Additional laboratory review or repeat analysis may occasionally extend the expected turnaround.

The Atypical Pneumonia Screen measures antibody responses rather than directly detecting Chlamydia pneumoniae, Mycoplasma pneumoniae or Legionella bacteria. This is important when interpreting positive and negative results.

An IgM-positive result may be compatible with a relatively recent immune response, but it does not automatically prove current active infection. IgM antibodies may take time to appear, can persist for a period after infection and can occasionally produce non-specific results.

An IgG-positive result may indicate previous exposure and can remain detectable long after an infection has resolved. In some clinical circumstances, comparison between samples taken at different times can be more informative than one isolated IgG result.

A negative antibody result does not completely exclude infection, particularly if testing was performed early in the illness before a measurable antibody response developed.

Legionella serology also requires careful clinical interpretation. When acute Legionnaires' disease is strongly suspected, urinary antigen testing, respiratory PCR or culture may sometimes be preferred depending on the clinical circumstances.

Results should be considered alongside symptoms, examination findings, duration of illness, chest imaging and any other microbiological tests. A positive result does not automatically establish the cause of pneumonia, while a negative result does not rule out every atypical respiratory infection.

London Blood Tests provides the C3 Complement blood test in London for people requiring targeted assessment of complement system activity.

The test costs £89.99 and measures one biomarker: C3 Complement.

C3 is central to the classical, lectin and alternative complement pathways and can provide useful information during investigation or monitoring of autoimmune, infectious and renal disease.

Clinic appointments are available alongside home and hotel phlebotomy depending on location and availability, providing flexible options for people looking for a private C3 Complement blood test in London.

C3 is frequently interpreted alongside C4 because the pattern of both proteins can help provide additional information about complement pathway activation.