Complement Component 4 (C4) Test

Measures complement component 4 (C4), a protein commonly used to help assess immune system activity, from a blood sample. Suits people with suspected autoimmune conditions or unexplained inflammation who want this single marker checked.

Sample: Blood
Collection: Venous draw at clinic or nurse visit
Results in: 1 day
Biomarkers: 1

Tests for

Compare Health Test Score Single-marker immune test with next-day results

£125.00

Buy now — £125.00

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Test specifications

Provider: Better2Know
Sample type: blood
Collection method: venous draw at clinic or nurse visit
Turnaround time: 1 day
Biomarkers tested: 1
At-home test: No
Doctor reviewed: No
Gender focus: Both

What's tested

1 biomarker as listed by Better2Know.

About this test

C4 is a protein involved in the complement system, part of the immune response that helps the body fight infections and clear immune complexes. Better2Know positions this test for people with suspected autoimmune conditions such as lupus or rheumatoid arthritis, unexplained inflammation or recurrent infections, or those monitoring kidney or liver conditions. Abnormal C4 levels can be associated with these conditions, though the test does not diagnose them on its own.

There is no formal comparison group listed for this test, but among the inflammation and autoimmunity tests we track, £125 for a single marker sits above the typical price, roughly 41% higher than the median for similarly sized tests.

Clarity scores well, since Better2Know publishes a detailed description, the marker, turnaround and collection options. Clinical depth is modest, in the 32nd percentile of inflammation tests we track, reflecting the single-marker scope. Results and follow-up is a weak point too, since results are not reviewed by a doctor as standard, despite Better2Know's own description recommending you discuss abnormal results with a healthcare provider.

Who is it for?

This suits you if a doctor or specialist has suggested checking your C4 levels specifically, for example as part of monitoring lupus, rheumatoid arthritis, or a kidney or liver condition, and you want a quick, single-marker result without a full autoimmune panel.

It is less suitable as a first port of call if you have general, unexplained symptoms, since a single complement marker will not give a full picture on its own, and there is no comparison data here for cheaper or broader alternatives to weigh it against; results are also not reviewed by a doctor as standard.

How it works

You give a venous blood sample at a Better2Know clinic or during a home nurse visit. The sample is analysed for complement component 4 (C4) protein levels, with results available within around 1 working day. Better2Know does not state that results are reviewed by a doctor as standard, though it recommends discussing any abnormal result with a healthcare provider and can arrange a private consultation.

Pros & cons

Pros

A single, focused marker, useful if C4 is specifically what you need checked rather than a wider panel.
Results are available within around 1 working day of your sample reaching the lab.
Booking a home nurse visit avoids a trip to the clinic for this test too.
Better2Know's own description explains what abnormal C4 levels can be associated with in plain terms.

Cons

At £125, it's priced about 41% above the typical cost for a similarly sized inflammation test.
Only one marker is tested, so it won't give a full picture of immune or autoimmune activity.
Better2Know does not review results with a doctor as standard.

Our editorial score

Compare Health Test Score Single-marker immune test with next-day results

Editorial confidence: 9.0/10

This £125 blood test measures complement component 4 (C4), a protein commonly used to help assess immune system activity, with results back within a day of the sample reaching the lab. It's priced 41% above the £88.63 median for similarly sized inflammation tests we track. Results are not reviewed by a doctor as standard.

Score breakdown

Clarity and documentation 9.0/10

The listing publishes a detailed description, the full biomarker list, a stated turnaround, clear collection options, the sample type; it does not state what the report looks like.
Clinical depth 6.4/10

1 biomarkers, placing it in the 32nd percentile of inflammation tests we track.
Collection convenience 6.0/10

Requires a venous draw at a clinic; a home nurse visit is offered; results in around 1 days, well ahead of the inflammation norm of 4.
Results and follow-up 3.0/10

Results are not doctor-reviewed and no consultation is included; the provider does not describe the report format.
Trust signals 6.5/10

Trustpilot 4.2 from 775 reviews; CQC registered; trading 18+ years.
Value for money 4.4/10

£125.00 against a median of £88.63 for the 26 similarly sized inflammation tests we track (+41%).

Calculated 13 September 2026 from the facts we hold about this test and provider, using our published scoring formula. Scores are not hand-edited.

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