What is the C1q Binding Immune Complex Test?

The C1q Binding Immune Complex test measures circulating immune complexes that have the ability to bind to C1q, a key protein in the classical complement pathway. Immune complexes are formed when antibodies bind to antigens, such as infectious agents or self-antigens.

In healthy individuals, immune complexes are efficiently cleared from the circulation. In autoimmune or inflammatory diseases, these complexes may accumulate and trigger complement activation, leading to tissue inflammation and damage. Measuring C1q-binding complexes helps identify abnormal immune complex formation and activity.

This test is particularly useful in evaluating immune complex–mediated diseases and monitoring disease activity in certain autoimmune conditions.

Why do I need a test for C1q Binding Immune Complexes?

You may need this test if symptoms suggest an immune complex–mediated autoimmune disorder or if standard autoimmune markers do not fully explain ongoing inflammation. Elevated immune complexes can contribute to systemic inflammation and organ involvement.

The test is often used alongside complement levels (C3, C4) and autoantibody testing to provide a clearer picture of immune system activity. It is especially helpful when disease activity fluctuates or when monitoring response to treatment.

Symptoms and scenarios where testing is recommended:

• Suspected systemic autoimmune disease
• Systemic lupus erythematosus (SLE) assessment
• Vasculitis investigation
• Persistent inflammation of unclear cause
• Immune-mediated kidney disease
• Monitoring autoimmune disease activity
• Unexplained rashes, joint pain or fatigue
• Abnormal complement levels

Benefits of the C1q Binding Immune Complex Test

·      Detects circulating immune complexes
Identifies immune complex involvement in disease processes.

·      Supports autoimmune disease assessment
Useful in conditions driven by immune complex deposition.

·      Helps monitor disease activity
Levels may rise during active disease or flares.

·      Complements C3 and C4 testing
Provides functional insight into complement activation.

·      Aids evaluation of vasculitis and lupus
Often elevated in immune complex–mediated disorders.

·      Supports investigation of unexplained inflammation
Adds clarity when standard markers are inconclusive.

·      Guides treatment monitoring
Changes may reflect response to immunosuppressive therapy.

·      Simple blood-based immunological test
Requires only a standard blood sample.

Step-by-Step: How Testing Works

Choose your preferred testing method

You can attend one of our UK partner clinics or arrange a home or hotel visit with a mobile phlebotomist.

Option 1 – In-Clinic Blood Draw

1. Select your nearest UK clinic and book an appointment.
2. A clinician or phlebotomist collects a venous blood sample.
3. The sample is analysed for C1q-binding immune complexes.
4. Results are delivered securely online.

Option 2 – Home or Hotel Phlebotomy (+£60)

1. Book a UK-wide home or hotel visit at a convenient time.
2. A trained phlebotomist collects your blood sample on-site.
3. The sample is packaged and transported to the laboratory.
4. Results are uploaded digitally without the need to travel.

Access your report

You can download and share your results with your GP, immunologist or rheumatologist.

Your Results Explained

Low / Negative Levels

Low or negative results indicate no significant circulating immune complexes detected.
This suggests immune complex–mediated disease is unlikely at the time of testing.

Normal Levels

Normal results reflect expected immune complex clearance and balanced immune activity.
This supports stable immune system function.

High Levels

Elevated C1q-binding immune complexes indicate increased immune complex formation.
This is commonly associated with active autoimmune disease, particularly systemic lupus erythematosus or vasculitis.
Results are interpreted alongside complement levels, autoantibodies and clinical findings.