C4 (Complement Component )
Assess a key protein in your immune defences.
Complement Component 4 (C4) is a protein that forms part of the complement system, a group of blood proteins that work together as part of your immune defences. The complement system helps the body fight infection, clear away damaged cells, and support the wider immune response. Measuring the level of C4 gives useful insight into how active this part of your immune system is.
What it can help assess
- Autoimmune conditions: C4 levels can fall when the complement system is being actively used up, as happens in conditions such as lupus (SLE). It is often used to help monitor disease activity.
- Angioedema: low C4 is a useful marker in investigating hereditary angioedema, a condition causing recurrent episodes of swelling.
- Kidney conditions: certain types of kidney inflammation (glomerulonephritis) can be associated with low C4 levels.
- Inflammation: as C4 is also an acute phase protein, levels can rise in response to infection or inflammation.
Why it matters
Measuring C4 helps give a picture of how active your complement system is. It is most often used alongside other tests, including Complement Component 3 (C3), to help investigate and monitor autoimmune conditions, recurrent swelling, and complement-related immune disorders.
C4
No special preparation required.
For blood tests, we recommend drinking plenty of water beforehand to ensure smooth sample collection. If you are taking any regular medication, continue to do so unless advised otherwise by your doctor.
Important Clinical Information:
This test is a screening tool to monitor and support your overall health. It does not replace your GP or Consultant.
Always discuss your test results, especially any abnormal results, with your GP, who can interpret them in the context of your medical history and overall health.