C3 & C4 Complement
Private C3 & C4 Complement blood test in London for £138, measuring two immune complement markers with results in around 1–2 business days.
Turnaround time
1-2 business days
Biomarkers count
2
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Overview of the C3 & C4 Complement
The C3 & C4 Complement blood test measures two of the most clinically useful proteins within the complement immune system: Complement Component 3 and Complement Component 4.
The complement system is a network of circulating proteins that helps identify pathogens, enhance antibody responses, clear immune complexes and regulate inflammatory activity.
C3 plays a central role in all major complement activation pathways, while C4 is involved primarily in the classical and lectin pathways.
The test contains 2 biomarkers: C3 Complement and C4 Complement.
Measuring both markers together provides more information than either result alone because the pattern of reduction can help clinicians assess how the complement system may be activated.
Low C3 and low C4 together can occur during classical pathway activation and are commonly associated with active immune-complex disease such as systemic lupus erythematosus.
Low C3 with relatively normal C4 may suggest alternative pathway activation and can occur in selected infections, post-infectious glomerulonephritis and disorders involving abnormal regulation of the alternative complement pathway.
Low C4 with relatively normal C3 may occur in immune-complex conditions, cryoglobulinaemia and hereditary or acquired C1 esterase inhibitor deficiency.
Both C3 and C4 can also increase during inflammatory responses because they behave as acute-phase proteins.
Results should therefore be interpreted alongside symptoms, medical history, kidney findings, autoimmune antibodies and previous complement measurements rather than in isolation.
What Does the C3 & C4 Complement Test Check?
This test measures 2 biomarkers.
C3 Complement
Measures Complement Component 3, a central protein shared by the classical, lectin and alternative complement pathways. Reduced concentrations can occur with complement consumption in autoimmune, infectious and renal conditions.
C4 Complement
Measures Complement Component 4, a protein involved primarily in the classical and lectin complement pathways. Reduced concentrations may occur with immune-complex disease, systemic lupus erythematosus, cryoglobulinaemia and C1 inhibitor deficiency.
Who May Benefit From the C3 & C4 Complement Test?
This combined test may be suitable for people undergoing investigation or monitoring of autoimmune, immune-complex, renal or complement-related conditions where the pattern of C3 and C4 provides useful additional information.
Suspected systemic lupus erythematosus - Both C3 and C4 can fall during active immune-complex disease.
Known lupus requiring monitoring - Serial complement measurements may provide useful information about disease activity and possible flares.
Possible immune-mediated kidney disease - C3 and C4 patterns can contribute to the investigation of selected forms of glomerulonephritis.
Possible vasculitis - Complement measurement may form part of a wider assessment where immune-complex vasculitis is suspected.
Recurrent unexplained swelling - The combination can help identify a low-C4 pattern that may prompt investigation of C1 esterase inhibitor deficiency.
Cryoglobulinaemia investigation - Low C4, sometimes with other complement abnormalities, can occur in cryoglobulin-related disease.
Previously abnormal complement levels - Repeat testing can help determine whether complement consumption persists or changes over time.
Recurrent or unusual infections - Complement testing may occasionally contribute to investigation where immune dysfunction is suspected.
Specialist-requested complement assessment - The test can be arranged privately where a rheumatologist, immunologist, nephrologist or GP has specifically requested both C3 and C4.
How to Prepare
Do not stop immunosuppressive medication or other prescribed treatment simply to alter complement concentrations unless specifically instructed.
Serial C3 and C4 measurements can be particularly useful when an established autoimmune condition is being monitored because changes over time may provide more information than one isolated result.
Symptoms and Reasons to Consider the C3 & C4 Complement Test
You may wish to consider the C3 & C4 Complement test when symptoms or previous investigations suggest autoimmune disease, immune-complex activity, inflammatory kidney disease or another complement-related condition.
Persistent joint pain or swelling - Joint symptoms can occur in autoimmune connective-tissue diseases associated with complement consumption.
Unexplained or recurrent skin rashes - Certain autoimmune and vasculitic conditions can produce persistent inflammatory skin changes.
Blood or protein detected in urine - Abnormal urine findings can lead to investigation for immune-mediated kidney disease.
Unexplained swelling of the legs or face - Oedema can occur in renal disease and warrants appropriate clinical assessment.
Recurrent unexplained angioedema - Episodes of swelling without typical allergy features may prompt assessment of C4 and C1 esterase inhibitor.
Previously positive autoimmune antibodies - C3 and C4 may provide additional information alongside ANA, dsDNA and other autoimmune markers.
Known lupus with changing symptoms - Falling complement levels may provide supporting information when a disease flare is suspected.
Recurrent infections or unexplained immune dysfunction - Complement testing can form part of a broader immunology assessment in selected cases.
These symptoms are not specific to abnormal complement levels and can occur with many autoimmune, infectious, allergic and renal conditions.
C3 and C4 results cannot independently diagnose lupus, vasculitis, hereditary angioedema or glomerulonephritis.
Significant swelling involving the tongue or throat, breathing difficulty, rapidly worsening kidney symptoms or severe systemic illness requires urgent medical assessment regardless of complement results.
How to Book Your C3 & C4 Complement Test
Booking your C3 & C4 Complement test with London Blood Tests is simple and designed to fit around your schedule.
Choose the C3 & C4 Complement
Select the C3 & C4 Complement test online and review the two included complement biomarkers before booking.
Select your sample collection option
Choose an in-clinic blood draw (+£35) or a home or hotel phlebotomy visit (+£60) where a qualified phlebotomist collects your sample.
Attend your appointment
A trained professional will collect your blood sample safely and efficiently at the clinic or during your arranged home or hotel visit.
Laboratory analysis
Your sample is sent to the laboratory, where C3 Complement and C4 Complement are measured using specialist immunology or biochemistry analysis.
Receive your results securely
Your results are sent securely by email, ready to review yourself or discuss with a GP, rheumatologist, immunologist, nephrologist or other suitably qualified healthcare professional.
When Will I Receive My Results?
The expected turnaround time for the C3 & C4 Complement test is approximately 1–2 business days after your sample arrives at the laboratory.
Results are sent securely by email once laboratory analysis and authorisation are complete.
Specialist review or repeat analysis may occasionally extend the expected turnaround.
Understanding Your Results
Your C3 & C4 Complement report shows the measured concentrations of both complement proteins together with the laboratory reference intervals.
Interpretation is based not only on whether each result is low or high but also on the pattern between the two markers.
Low C3 and low C4 together can indicate activation of the classical complement pathway and may occur in active immune-complex disease such as SLE.
Low C3 with a relatively normal C4 may suggest alternative pathway activation. This pattern can occur with selected infections, post-infectious glomerulonephritis and some disorders involving C3 regulation.
Low C4 with a relatively normal C3 can occur with cryoglobulinaemia, selected immune-complex disorders and hereditary or acquired C1 esterase inhibitor deficiency.
Normal complement concentrations do not completely exclude autoimmune disease because C3 and C4 are also acute-phase proteins and their production may increase during inflammation.
High concentrations are generally non-specific and may reflect an inflammatory response rather than a primary complement disorder.
Serial measurements are often particularly useful in established SLE because changes from a person's previous baseline can provide more information than a single result.
Results should therefore be interpreted alongside symptoms, kidney function, urine findings, autoimmune antibodies and other immunology investigations.
Why Book With London Blood Tests?
Private C3 and C4 testing in London - Access combined complement assessment through London Blood Tests.
Two complementary immune markers - Measure both C3 and C4 in one test for a broader view of complement activity.
Relevant to lupus investigation and monitoring - Both markers are commonly used when assessing systemic lupus erythematosus.
Useful for complement pathway interpretation - Different C3 and C4 patterns can provide additional information about classical and alternative pathway activity.
Relevant to immune-mediated kidney disease - Combined complement measurement can form part of selected glomerulonephritis investigations.
Useful in angioedema assessment - A low-C4 pattern can prompt additional C1 esterase inhibitor testing where hereditary angioedema is suspected.
Clinic and home visit options - Choose an in-clinic blood draw or arrange home or hotel phlebotomy depending on location and availability.
Secure results by email - Receive your authorised laboratory result securely once analysis is complete.
Clear pricing before booking - The C3 & C4 Complement test is priced at £138, with sample collection charges shown separately.
Private C3 & C4 Complement Blood Test in London
London Blood Tests provides the C3 & C4 Complement blood test in London for people requiring a combined assessment of two important complement proteins.
The test costs £138 and measures two biomarkers: C3 Complement and C4 Complement.
Testing both markers together provides additional information because different patterns of C3 and C4 reduction can occur with different forms of immune and complement activation.
Clinic appointments are available alongside home and hotel phlebotomy depending on location and availability, providing flexible options for people looking for a private C3 and C4 Complement blood test in London.
Results should be interpreted alongside symptoms, autoimmune antibodies, renal investigations and previous complement measurements where available.