What is the Complement C1q test?

The Complement C1q test measures the level of Complement Component 1q, a protein that initiates the classical complement pathway. The complement system is part of the innate immune response and plays a critical role in identifying and clearing pathogens and immune complexes.

C1q binds to antibodies attached to antigens, triggering a cascade of immune activation that helps eliminate infections and regulate inflammation. Adequate C1q levels are essential for effective immune surveillance and immune complex clearance.

This test is commonly used in immunology and rheumatology when investigating autoimmune disease, immune complex disorders, or suspected complement deficiencies.

Why do I need a Complement C1q test?

Abnormal C1q levels can be associated with autoimmune diseases, immune complex–mediated conditions, or rare inherited complement deficiencies. Testing helps clarify whether the classical complement pathway is functioning normally.

You may need a Complement C1q test if you:

• Have suspected autoimmune disease
• Have recurrent or severe infections
• Have unexplained inflammation
• Have low complement levels on other tests
• Are being investigated for lupus or related conditions
• Have symptoms suggesting immune complex disease
• Require detailed immune system assessment

Symptoms that may prompt testing include:

• Persistent fatigue
• Joint pain or swelling
• Skin rashes
• Recurrent infections
• Unexplained inflammatory symptoms

Benefits of the Complement C1q test

• Assesses classical complement pathway function
  Evaluates a key immune activation step.
• Supports autoimmune disease investigation
  Relevant in immune complex disorders.
• Useful in recurrent infection assessment
  Helps identify complement-related immune issues.
• Clinically recognised immune marker
  Used in specialist immunology testing.
• Supports diagnosis of rare complement deficiencies
  Identifies abnormal complement activity.
• Simple blood test
  Requires only a single blood sample.
• Guides further immune investigations
  Helps determine need for additional complement testing.
• Improves diagnostic clarity
  Aids understanding of immune dysfunction.

Step by step – how the test works

You can access Complement C1q testing UK-wide through two options:

1. Clinic appointment
   Choose your nearest UK clinic, where a healthcare professional will take your blood sample.
2. At-home or hotel visit (£60 extra)
   A qualified phlebotomist visits your home or hotel, so you don’t need to travel.

Your sample is analysed in an accredited UK laboratory, and results are delivered securely.

Your results explained

Low Complement C1q levels

May indicate complement deficiency or consumption due to immune complex activity, often seen in autoimmune conditions.

Typical UK interpretation:

• Below laboratory reference range

Normal Complement C1q levels

Suggest intact classical complement pathway function.

Typical UK interpretation:

• Within laboratory reference range

High Complement C1q levels

May be associated with acute inflammation or immune activation.

Typical UK interpretation:

• Above laboratory reference range

Reference ranges vary between laboratories and must be interpreted clinically.